TCF Financial 10-Q 24 Oct 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014	Oct. 17, 2014
Entity Information [Line Items]	'	'
Entity Registrant Name	'CHEMICAL FINANCIAL CORP	'
Entity Central Index Key	'0000019612	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-14	'
Amendment Flag	'false	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	32,762,591

Consolidated_Statements_of_Fin

Consolidated Statements of Financial Position (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Cash and cash equivalents:	'	'	'
Cash and cash due from banks	$134,116	$130,811	$135,839
Interest-bearing deposits with the Federal Reserve Bank	248,022	179,977	357,271
Total cash and cash equivalents	382,138	310,788	493,110
Investment securities:	'	'	'
Available-for-sale, at fair value	576,211	684,570	705,146
Held-to-maturity (fair value - $314,275 at September 30, 2014, $268,271 at December 31, 2013 and $275,866 at September 30, 2013)	318,562	273,905	282,579
Total investment securities	894,773	958,475	987,725
Loans held-for-sale, at fair value	9,347	5,219	7,907
Loans	5,040,920	4,647,621	4,522,671
Allowance for loan losses	-77,006	-79,072	-81,532
Net loans	4,963,914	4,568,549	4,441,139
Premises and equipment (net of accumulated depreciation of $106,418 at September 30, 2014, $100,261 at December 31, 2013 and $98,150 at September 30, 2013)	80,127	75,308	73,690
Goodwill	120,164	120,164	120,164
Other intangible assets	11,958	13,424	13,865
Interest receivable and other assets	134,564	132,781	120,636
Total Assets	6,596,985	6,184,708	6,258,236
Deposits:	'	'	'
Noninterest-bearing	1,344,716	1,227,768	1,162,599
Interest-bearing	4,087,211	3,894,617	4,028,706
Total deposits	5,431,927	5,122,385	5,191,305
Interest payable and other liabilities	40,366	38,395	36,019
Short-term borrowings	323,086	327,428	357,595
Total liabilities	5,795,379	5,488,208	5,584,919
Shareholders’ equity:	'	'	'
Preferred stock, no par value: Authorized - 200,000 shares, none issued	0	0	0
Issued and outstanding — 32,762,591 shares at September 30, 2014, 29,789,825 shares at December 31, 2013 and 29,778,250 shares at September 30, 2013	32,763	29,790	29,778
Additional paid-in capital	564,127	488,177	487,176
Retained earnings	224,222	199,053	191,538
Accumulated other comprehensive loss	-19,506	-20,520	-35,175
Total shareholders’ equity	801,606	696,500	673,317
Total Liabilities and Shareholders’ Equity	$6,596,985	$6,184,708	$6,258,236

Consolidated_Statements_of_Fin1

Consolidated Statements of Financial Position (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, except Share data, unless otherwise specified
Held-to-maturity, fair value	$314,275	$268,271	$275,866
Accumulated depreciation of premises and equipment	$106,418	$100,261	$98,150
Preferred stock, no par value	'	'	'
Preferred stock, shares authorized	200,000	200,000	200,000
Preferred stock, shares issued	0	0	0
Common stock, par value	$1	$1	$1
Common stock, shares authorized	45,000,000	45,000,000	45,000,000
Common stock, shares issued	32,762,591	29,789,825	29,778,250
Common stock, shares outstanding	32,762,591	29,789,825	29,778,250

Consolidated_Statements_of_Inc

Consolidated Statements of Income (Unaudited) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Interest Income	'	'	'	'
Interest and fees on loans	$52,343	$49,017	$152,289	$144,951
Interest on investment securities:	'	'	'	'
Taxable	2,194	2,714	6,825	7,737
Tax-exempt	1,838	1,587	5,213	4,738
Dividends on nonmarketable equity securities	160	150	809	701
Interest on deposits with the Federal Reserve Bank	94	110	318	611
Total interest income	56,629	53,578	165,454	158,738
Interest Expense	'	'	'	'
Interest on deposits	3,469	4,160	10,840	12,990
Interest on short-term borrowings	92	124	307	359
Interest on Federal Home Loan Bank (FHLB) advances	0	0	0	47
Total interest expense	3,561	4,284	11,147	13,396
Net Interest Income	53,068	49,294	154,307	145,342
Provision for loan losses	1,500	3,000	4,600	9,000
Net interest income after provision for loan losses	51,568	46,294	149,707	136,342
Noninterest Income	'	'	'	'
Service charges and fees on deposit accounts	5,612	5,690	16,028	16,420
Wealth management revenue	3,730	3,369	11,319	10,693
Other charges and fees for customer services	4,686	4,272	13,562	13,226
Mortgage banking revenue	1,166	1,038	3,451	4,699
Gain on sale of investment securities	0	0	0	1,104
Other	157	275	508	689
Total noninterest income	15,351	14,644	44,868	46,831
Operating Expenses	'	'	'	'
Salaries, wages and employee benefits	24,885	24,065	73,929	72,062
Occupancy	3,629	3,406	11,641	10,449
Equipment and software	3,772	3,354	11,025	10,251
Other	10,416	8,720	30,714	29,781
Total operating expenses	42,702	39,545	127,309	122,543
Income before income taxes	24,217	21,393	67,266	60,630
Federal income tax expense	7,450	6,400	20,450	18,200
Net Income	$16,767	$14,993	$46,816	$42,430
Net Income Per Common Share:	'	'	'	'
Basic (in dollars per share)	$0.51	$0.54	$1.52	$1.54
Diluted (in dollars per share)	$0.51	$0.53	$1.51	$1.53
Cash Dividends Declared Per Common Share (dollars per share)	$0.24	$0.22	$0.70	$0.64

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Unaudited) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net income	$16,767	$14,993	$46,816	$42,430
Other comprehensive income (loss), net of tax:	'	'	'	'
Net unrealized gains (losses) on investment securities available-for-sale, net of tax expense (benefit) of $(615) and $(392) for the three months ended September 30, 2014 and 2013, respectively, and $1,150 and $(2,879) for the nine months ended September 30, 2014 and 2013, respectively	-1,144	-726	2,136	-5,347
Reclassification adjustment for realized gain on sale of investment securities available-for-sale included in net income, net of tax expense of $300 for the nine months ended September 30, 2013	0	0	0	-558
Adjustment for pension and other postretirement benefits, net of tax expense (benefit) of $(201) and $332 for the three months ended September 30, 2014 and 2013, respectively, and $(604) and $996 for the nine months ended September 30, 2014 and 2013, respectively	-374	616	-1,122	1,849
Total other comprehensive income (loss), net of tax	-1,518	-110	1,014	-4,056
Comprehensive income	$15,249	$14,883	$47,830	$38,374

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Tax expense (benefit) on net unrealized gains (losses) on investment securities available-for-sale	($615)	($392)	$1,150	($2,879)
Tax expense (benefit) on reclassification adjustment for realized gains on sale of investment securities available-for-sale	0	0	0	-300
Tax expense (benefit) on adjustment for pension and other postretirement benefits	($201)	$332	($604)	$996

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (USD $)	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
In Thousands, unless otherwise specified
Beginning Balance at Dec. 31, 2012	$596,341	$27,499	$433,195	$166,766	($31,119)
Changes in Stockholders' Equity [Roll Forward]	'	'	'	'	'
Comprehensive income	38,374	'	'	42,430	-4,056
Cash dividends declared per share: $0.64 and $0.70 per share for the nine months ended September 30, 2013 and September 30, 2014, respectively	-17,658	'	'	-17,658	'
Issuance of common stock, net of issuance costs	53,925	2,214	51,711	'	'
Stock issued - stock options	278	29	249	'	'
Shares issued – directors’ stock plans	305	13	292	'	'
Shares issued – restricted stock units	-379	23	-402	'	'
Share-based compensation	2,131	'	2,131	'	'
Ending Balance at Sep. 30, 2013	673,317	29,778	487,176	191,538	-35,175
Beginning Balance at Dec. 31, 2013	696,500	29,790	488,177	199,053	-20,520
Changes in Stockholders' Equity [Roll Forward]	'	'	'	'	'
Comprehensive income	47,830	'	'	46,816	1,014
Cash dividends declared per share: $0.64 and $0.70 per share for the nine months ended September 30, 2013 and September 30, 2014, respectively	-21,647	'	'	-21,647	'
Issuance of common stock, net of issuance costs	76,175	2,875	73,300	'	'
Stock issued - stock options	901	43	858	'	'
Shares issued – directors’ stock plans	468	18	450	'	'
Shares issued – restricted stock units	-502	37	-539	'	'
Share-based compensation	1,881	'	1,881	'	'
Ending Balance at Sep. 30, 2014	$801,606	$32,763	$564,127	$224,222	($19,506)

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Cash dividends declared per share	$0.24	$0.22	$0.70	$0.64

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (Unaudited) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Operating Activities	'	'
Net income	$46,816	$42,430
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Provision for loan losses	4,600	9,000
Gains on sales of loans	-3,137	-6,041
Proceeds from sales of loans	105,870	181,644
Loans originated for sale	-106,861	-165,845
Net gains on sales of other real estate and repossessed assets	-1,443	-2,265
Depreciation of premises and equipment	6,431	6,552
Amortization of intangible assets	2,211	2,794
Gain on sale of investment securities	0	-1,104
Net amortization of premiums and discounts on investment securities	3,183	3,054
Share-based compensation expense	1,881	2,131
Contributions to defined benefit pension plan	0	-15,000
Net (increase) decrease in interest receivable and other assets	-2,297	6,634
Net increase (decrease) in interest payable and other liabilities	403	-786
Net cash provided by operating activities	57,657	63,198
Investment securities – available-for-sale:	'	'
Proceeds from sales	0	38,028
Proceeds from maturities, calls and principal reductions	109,004	121,959
Purchases	0	-289,189
Investment securities – held-to-maturity:	'	'
Proceeds from maturities, calls and principal reductions	75,168	51,962
Purchases	-120,367	-104,733
Net increase in loans	-407,835	-371,423
Proceeds from sales of other real estate and repossessed assets	8,735	13,229
Purchases of premises and equipment and branch bank property, net of disposals	-11,250	-5,166
Net cash used in investing activities	-346,545	-545,333
Financing Activities	'	'
Net increase in interest- and noninterest-bearing demand deposits and savings accounts	401,440	393,262
Net decrease in time deposits	-91,898	-123,400
Net increase (decrease) in short-term borrowings	-4,342	47,132
Repayment of FHLB advances	0	-34,289
Cash dividends paid	-21,647	-17,658
Proceeds from issuance of common stock, net of issuance costs	76,175	53,925
Proceeds from directors’ stock plans and exercise of stock options, net of shares withheld	1,211	517
Cash paid for payroll taxes upon conversion of restricted stock units	-701	-379
Net cash provided by financing activities	360,238	319,110
Net increase (decrease) in cash and cash equivalents	71,350	-163,025
Cash and cash equivalents at beginning of period	310,788	656,135
Cash and cash equivalents at end of period	382,138	493,110
Supplemental Disclosure of Cash Flow Information:	'	'
Interest paid	11,305	13,888
Loans transferred to other real estate and repossessed assets	7,870	4,528
Closed branch offices transferred to other real estate	0	382
Income Taxes Paid, Net	$19,900	$12,950

Significant_Accounting_Policie

Significant Accounting Policies	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Significant Accounting Policies	'
	Significant Accounting Policies
	Nature of Operations
	Chemical Financial Corporation (Corporation) operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operates through one commercial bank, Chemical Bank. Chemical Bank operates within the State of Michigan as a state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of four regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the bank’s geographical market areas. The products and services offered by the regional banking units, through branch banking offices, are generally consistent throughout the Corporation, as is the pricing of those products and services. The marketing of products and services throughout the Corporation’s regional banking units is generally uniform, as many of the markets served by the regional banking units overlap. The distribution of products and services is uniform throughout the Corporation’s regional banking units and is achieved primarily through retail branch banking offices, automated teller machines and electronically accessed banking products.
	The Corporation’s primary sources of revenue are interest from its loan products and investment securities, service charges and fees from customer deposit accounts and wealth management revenue.
	Basis of Presentation
	The accompanying unaudited consolidated financial statements of the Corporation and its subsidiaries have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, the interim consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s consolidated financial statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2013. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments believed necessary to present fairly the financial condition and results of operations of the Corporation for the periods presented. Operating results for the nine months ended September 30, 2014 are not necessarily indicative of the results that may be expected for the year ending December 31, 2014.
	Use of Estimates
	Management makes estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying footnotes. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, expected cash flows from acquired loans, fair value amounts related to business combinations, pension expense, income taxes, goodwill impairment and those assets that require fair value measurement. Actual results could differ from these estimates.
	Originated Loans
	Originated loans include all of the Corporation's portfolio loans, excluding loans acquired on April 30, 2010 in the acquisition of O.A.K. Financial Corporation (OAK). Originated loans also include loans acquired as part of the Corporation's branch acquisition on December 7, 2012, as these loans were performing and were considered high-quality loans in accordance with the Corporation's credit underwriting standards at that date. Originated loans are stated at their principal amount outstanding, net of unearned income, charge-offs and unamortized deferred fees and costs. Loan interest income is recognized on the accrual basis. Deferred loan fees and costs are amortized over the loan term based on the level-yield method. Net loan commitment fees are deferred and amortized into fee income on a straight-line basis over the commitment period.
	The past due status of a loan is based on the loan’s contractual terms. A loan is placed in nonaccrual status (accrual of interest is discontinued) when principal or interest is past due 90 days or more (except for a loan that is secured by residential real estate, which is transferred to nonaccrual status at 120 days past due), unless the loan is both well-secured and in the process of collection, or earlier when, in the opinion of management, there is sufficient reason to doubt the collectibility of principal or interest. Interest previously accrued, but not collected, is reversed and charged against interest income at the time the loan is placed in nonaccrual status. Subsequent receipts of interest while a loan is in nonaccrual status are recorded as a reduction of principal. Loans are returned to accrual status when principal and interest payments are brought current, payments have been received consistently for a period of time (generally six months) and collectibility is no longer in doubt.
	Loans Acquired in a Business Combination
	Loans acquired in a business combination (acquired loans) consist of loans acquired on April 30, 2010 in the acquisition of OAK. Acquired loans were recorded at fair value at the date of acquisition, without a carryover of the associated allowance for loan losses related to these loans, through a fair value discount that was, in part, attributable to deterioration in credit quality. The estimate of expected credit losses was determined based on due diligence performed by executive and senior officers of the Corporation, with assistance from third-party consultants. The fair value discount was recorded as a reduction of the acquired loans’ outstanding principal balances in the consolidated statement of financial position at the acquisition date.
	The Corporation accounts for acquired loans, which are recorded at fair value at acquisition, in accordance with Accounting Standards Codification (ASC) Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality (ASC 310-30). ASC 310-30 allows investors to aggregate loans acquired into loan pools that have common risk characteristics and thereby use a composite interest rate and expectation of cash flows expected to be collected for the loan pools. Under the provisions of ASC 310-30, the Corporation aggregated acquired loans into 14 pools based upon common risk characteristics, including types of loans, commercial type loans with similar risk grades and whether loans were performing or nonperforming. A pool is considered a single unit of accounting for purposes of applying the guidance prescribed in ASC 310-30. A loan will be removed from a pool of acquired loans only if the loan is sold, foreclosed, paid off or written off, and will be removed from the pool at the carrying value. If an individual loan is removed from a pool of loans, the difference between its relative carrying amount and the cash, fair value of the collateral, or other assets received would not affect the effective yield used to recognize the accretable difference on the remaining pool. The Corporation estimated the cash flows expected to be collected over the life of the pools of loans at acquisition, and estimates expected cash flows quarterly thereafter, based on a set of assumptions including expectations as to default rates, prepayment rates and loss severities. The Corporation must make numerous assumptions, interpretations and judgments using internal and third-party credit quality information to determine whether it is probable that the Corporation will be able to collect all contractually required payments. This is a point in time assessment and inherently subjective due to the nature of the available information and judgment involved.
	The calculation of the fair value of the acquired loan pools entails estimating the amount and timing of cash flows attributable to both principal and interest expected to be collected on such loan pools and then discounting those cash flows at market interest rates. The excess of a loan pool's expected cash flows at the acquisition date over its estimated fair value is referred to as the "accretable yield," which is recognized into interest income over the estimated remaining life of the loan pool on a level-yield basis. The difference between a loan pool's contractually required principal and interest payments at the acquisition date and the cash flows expected to be collected at the acquisition date is referred to as the "nonaccretable difference," which includes an estimate of future credit losses expected to be incurred over the estimated life of the loan pool and interest payments that are not expected to be collected. Decreases to the expected cash flows in each loan pool in subsequent periods will require the Corporation to record a provision for loan losses. Improvements in expected cash flows in each loan pool in subsequent periods will result in reversing a portion of the nonaccretable difference, which is then classified as part of the accretable yield and subsequently recognized into interest income over the estimated remaining life of the loan pool.
	Loans Modified Under Troubled Debt Restructurings
	Loans modified under troubled debt restructurings (TDRs) involve granting a concession to a borrower who is experiencing financial difficulty. Concessions generally include modifications to original loan terms, including changes to a loan’s payment schedule or interest rate, which generally would not otherwise be considered. The Corporation’s TDRs include performing and nonperforming TDRs, which consist of originated loans that continue to accrue interest at the loan's original interest rate as the Corporation expects to collect the remaining principal and interest on the loan, and nonaccrual TDRs, which include originated loans that are in a nonaccrual status and are no longer accruing interest, as the Corporation does not expect to collect the full amount of principal and interest owed from the borrower on these loans. At the time of modification (except for loans on nonaccrual status), a TDR is reported as a nonperforming TDR until a six-month payment history of principal and interest payments, in accordance with the terms of the loan modification, is sustained, at which time the Corporation moves the loan to a performing status (performing TDR). If the Corporation does not expect to collect all principal and interest on the loan, the modified loan is classified as a nonaccrual TDR. All TDRs are accounted for as impaired loans and are included in the Corporation’s analysis of the allowance for loan losses. A TDR that has been refinanced by a borrower who is no longer experiencing financial difficulty and which yields a market rate of interest at the time of a refinancing is no longer reported as a TDR.
	Loans in the Corporation’s commercial loan portfolio (comprised of commercial, commercial real estate, real estate construction and land development loans) that meet the definition of a TDR generally consist of loans where the Corporation has allowed borrowers to defer scheduled principal payments and make interest-only payments for a specified period of time at the stated interest rate of the original loan agreement or reduced payments due to a moderate extension of the loan’s contractual term. If the Corporation does not expect to collect all principal and interest on the loan, the modified loan is classified as a nonaccrual TDR. If the Corporation does not expect to incur a loss on the loan based on its assessment of the borrowers’ expected cash flows, as the pre- and post-modification effective yields are approximately the same, the loan is classified as a nonperforming TDR until a six-month payment history is sustained, at which time the loan is classified as a performing TDR. Since no loss is expected to be incurred on these loans, no additional provision for loan losses has been recognized related to these loans, and these loans accrue interest at their contractual interest rate. These loans are individually evaluated for impairment and transferred to nonaccrual status if they become 90 days past due as to principal or interest payments or if it is probable that any remaining principal and interest payments due on the loan will not be collected in accordance with the modified terms of the loans.
	Loans in the Corporation’s consumer loan portfolio (comprised of residential mortgage, consumer installment and home equity loans) that meet the definition of a performing or nonperforming TDR generally consist of residential mortgage loans that include a concession that reduces a borrower’s monthly payments by decreasing the interest rate charged on the loan for a specified period of time (generally 24 months) under a formal modification agreement. The Corporation recognizes an additional provision for loan losses related to impairment on these loans on an individual basis based on the present value of expected future cash flows discounted at the loan’s original effective interest rate. These loans continue to accrue interest at the loan's effective interest rate, which consists of contractual interest under the terms of the modification agreement in addition to an adjustment for the accretion of computed impairment. These loans are moved to nonaccrual status if they become 90 days past due as to principal or interest payments, or sooner if conditions warrant.
	Impaired Loans
	A loan is defined to be impaired when it is probable that payment of principal and interest will not be paid in accordance with the original contractual terms of the loan agreement. Impaired loans include nonaccrual loans (including nonaccrual TDRs), performing and nonperforming TDRs and acquired loans that were not performing in accordance with original contractual terms. Impaired loans are accounted for at the lower of the present value of expected cash flows discounted at the loan's original effective interest rate or the estimated fair value of the collateral, if the loan is collateral dependent. When the present value of expected cash flows or the fair value of collateral of an impaired loan in the originated loan portfolio is less than the amount of unpaid principal outstanding on the loan, the principal balance of the loan is reduced to its carrying value through either an allocation of the allowance for loan losses or a partial charge-off of the loan balance.
	Nonperforming Loans
	Nonperforming loans are comprised of loans for which the accrual of interest has been discontinued (nonaccrual loans, including nonaccrual TDRs), accruing originated loans contractually past due 90 days or more as to interest or principal payments and nonperforming TDRs.
	Acquired loans that were classified as nonperforming loans prior to being acquired and acquired loans that are not performing in accordance with contractual terms subsequent to acquisition are not classified as nonperforming loans subsequent to acquisition because the loans are recorded in pools at net realizable value based on the principal and interest the Corporation expects to collect on such loans.
	Allowance for Loan Losses
	The allowance for loan losses (allowance) is presented as a reserve against loans. The allowance represents management’s assessment of probable loan losses inherent in the Corporation’s loan portfolio.
	Management’s evaluation of the adequacy of the allowance is based on a continuing review of the loan portfolio, actual loan loss experience, the underlying value of the collateral, risk characteristics of the loan portfolio, the level and composition of nonperforming loans, the financial condition of the borrowers, the balance of the loan portfolio, loan growth, economic conditions, employment levels in the Corporation’s local markets, and special factors affecting specific business sectors. The Corporation maintains formal policies and procedures to monitor and control credit risk. Management evaluates the allowance on a quarterly basis in an effort to ensure the level is appropriate to absorb probable losses inherent in the loan portfolio.
	The allowance provides for probable losses that have been identified with specific customer relationships and for probable losses believed to be incurred in the remainder of the originated loan portfolio, but that have not been specifically identified. The Corporation utilizes its own loss experience to estimate inherent losses on loans. Internal risk ratings are assigned to each loan in the commercial loan portfolio (commercial, commercial real estate, real estate construction and land development loans) at the time of origination and are subject to subsequent periodic reviews by senior management. The Corporation performs a detailed credit quality review quarterly on all loans greater than $0.25 million that have deteriorated below certain levels of credit risk, and may allocate a specific portion of the allowance to such loans based upon this review. A portion of the allowance is allocated to the remaining loans by applying projected loss ratios, based on numerous factors. Projected loss ratios incorporate factors such as charge-off experience, trends with respect to adversely risk-rated loans in the commercial loan portfolio, trends with respect to past due and nonaccrual loans, changes in economic conditions and trends, changes in the value of underlying collateral and other credit risk factors. This evaluation involves a high degree of uncertainty.
	In determining the allowance and the related provision for loan losses, the Corporation considers four principal elements: (i) valuation allowances based upon probable losses identified during the review of impaired loans in the commercial loan portfolio, (ii) reserves established for adversely-rated loans in the commercial loan portfolio and nonaccrual residential mortgage, consumer installment and home equity loans based on loan loss experience of other adversely-rated loans, (iii) reserves, by loan classes, on all other loans based principally on a five-year historical loan loss experience, with higher weighting placed on the most recent years, and loan loss trends and (iv) an unallocated allowance based on the imprecision in the overall allowance methodology for loans collectively evaluated for impairment.
	Although the Corporation allocates portions of the allowance to specific loans and loan types, the entire allowance attributable to originated loans is available for any loan losses that occur in the originated portfolio. Loans that are deemed not collectible are charged off and reduce the allowance. The provision for loan losses and recoveries on loans previously charged off increase the allowance. Collection efforts may continue and recoveries may occur after a loan is charged off.
	Acquired loans are aggregated into pools based upon common risk characteristics. An allowance may be recorded related to an acquired loan pool if it experiences a decrease in expected cash flows, as compared to those projected at the acquisition date. On a quarterly basis, the expected future cash flow of each pool is estimated based on various factors, including changes in property values of collateral dependent loans, default rates, loss severities and prepayment speeds. Decreases in estimates of expected cash flows within a pool generally result in a charge to the provision for loan losses and a corresponding increase in the allowance allocated to acquired loans for the particular pool. Increases in estimates of expected cash flows within a pool generally result in a reduction in the allowance allocated to acquired loans for the particular pool, if applicable, and then an adjustment to the accretable yield for the pool, which will increase amounts recognized in interest income in subsequent periods.
	Various regulatory agencies, as an integral part of their examination process, periodically review the allowance. Such agencies may require additions to the allowance, based on their judgment, reflecting information available to them at the time of their examinations.
	Fair Value Measurements
	Fair value for assets and liabilities measured at fair value on a recurring or nonrecurring basis refers to the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants in the market in which the reporting entity transacts such sales or transfers based on the assumptions market participants would use when pricing an asset or liability. Assumptions are developed based on prioritizing information within a fair value hierarchy that gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data, such as the reporting entity’s own data.
	The Corporation may choose to measure eligible items at fair value at specified election dates. Unrealized gains and losses on items for which the fair value measurement option has been elected are reported in earnings at each subsequent reporting date. The fair value option (i) may be applied instrument by instrument, with certain exceptions, allowing the Corporation to record identical financial assets and liabilities at fair value or by another measurement basis permitted under GAAP, (ii) is irrevocable (unless a new election date occurs) and (iii) is applied only to entire instruments and not to portions of instruments. At September 30, 2014, December 31, 2013 and September 30, 2013, the Corporation had elected the fair value option on all of its residential mortgage loans held-for-sale. The Corporation has not elected the fair value option for any other financial assets or liabilities.
	Share-Based Compensation
	The Corporation grants stock options, stock awards, restricted stock performance units and restricted stock service-based units to certain executive and senior management employees. The Corporation accounts for share-based compensation expense using the modified-prospective transition method. Under that method, compensation expense is recognized for stock options based on the estimated grant date fair value as computed using the Black-Scholes option pricing model and the probability of issuance. The Corporation accounts for stock awards based on the closing stock price of the Corporation's common stock on the date of the award. The fair values of both stock options and stock awards are recognized as compensation expense on a straight-line basis over the requisite service period. The Corporation accounts for restricted stock performance units based on the closing stock price of the Corporation's common stock on the date of grant, discounted by the present value of estimated future dividends to be declared over the requisite performance or service period. The fair value of restricted stock performance units is recognized as compensation expense over the expected requisite performance period, or requisite service period for awards with multiple performance and service conditions. The Corporation accounts for restricted stock service-based units based on the closing stock price of the Corporation's common stock on the date of grant, as these awards accrue dividend equivalents equal to the amount of any cash dividends that would have been payable to a shareholder owning the number of shares of the Corporation's common stock represented by the restricted stock service-based units. The fair value of the restricted stock service-based units is recognized as compensation expense over the requisite service period.
	Cash flows realized from the tax benefits of exercised stock option awards that result from actual tax deductions that are in excess of the recorded tax benefits related to the compensation expense recognized for those options (excess tax benefits) are classified as financing activities on the consolidated statements of cash flows.
	Income and Other Taxes
	The Corporation is subject to the income and other tax laws of the United States, the State of Michigan and other states where nexus has been created. These laws are complex and are subject to different interpretations by the taxpayer and the various taxing authorities. In determining the provision for income and other taxes, management must make judgments and estimates about the application of these inherently complex laws, related regulations and case law. In the process of preparing the Corporation’s tax returns, management attempts to make reasonable interpretations of enacted tax laws. These interpretations are subject to challenge by the tax authorities upon audit or to reinterpretation based on management’s ongoing assessment of facts and evolving case law.
	On a quarterly basis, management assesses the reasonableness of its estimated annual effective federal tax rate based upon its current best estimate of taxable income and the applicable taxes expected for the full year. Deferred tax assets and liabilities are reassessed on a quarterly basis, including the need for a valuation allowance for deferred tax assets.
	Uncertain income tax positions are evaluated to determine whether it is more-likely-than-not that a tax position will be sustained upon examination based on the technical merits of the tax position. If a tax position is more-likely-than-not to be sustained, a tax benefit is recognized for the amount that is greater than 50% likely to be realized. Reserves for contingent income tax liabilities attributable to unrecognized tax benefits associated with uncertain tax positions are reviewed quarterly for adequacy based upon developments in tax law and the status of audits or examinations. The Corporation had no contingent income tax liabilities recorded at September 30, 2014, December 31, 2013 or September 30, 2013. The tax periods open to examination by the Internal Revenue Service include the calendar years ended December 31, 2013, 2012 and 2011.
	Shareholders’ Equity
	Common Stock Repurchase Programs
	From time to time, the board of directors of the Corporation approves common stock repurchase programs allowing management to repurchase shares of the Corporation’s common stock in the open market. The repurchased shares are available for later reissuance in connection with potential future stock dividends, the Corporation’s dividend reinvestment plan, employee benefit plans and other general corporate purposes. Under these programs, the timing and actual number of shares subject to repurchase are at the discretion of management and are contingent on a number of factors, including the projected parent company cash flow requirements and the Corporation’s market price per share.
	In January 2008, the board of directors of the Corporation authorized the repurchase of up to 500,000 shares of the Corporation’s common stock under a stock repurchase program. In November 2011, the board of directors of the Corporation reaffirmed the stock buy-back authorization with the qualification that the shares may only be repurchased if the share price is below the tangible book value per share of the Corporation’s common stock at the time of the repurchase. Since the January 2008 authorization, no shares have been repurchased. At September 30, 2014, there were 500,000 remaining shares available for repurchase under the Corporation’s stock repurchase programs.
	Underwritten Public Offerings of Common Stock
	On June 24, 2014, the Corporation issued and sold 2,500,000 shares of common stock at a public offering price of $28.00 per share. An additional 375,000 shares were issued and sold on June 30, 2014 upon the exercise in full of the underwriters' over-allotment option. The net proceeds from the issuance and sale of the common stock, after deducting the underwriting discount and issuance-related expenses, totaled $76.2 million.
	On September 18, 2013, the Corporation issued and sold 2,213,750 shares of common stock, including 288,750 shares of common stock that were issued and sold upon the exercise in full of the underwriters' over-allotment option, at a public offering price of $26.00 per share. The net proceeds from the issuance and sale of the common stock, after deducting the underwriting discount and issuance-related expenses, totaled $53.9 million.
	Shelf Registration
	On June 12, 2014, the Corporation filed an automatic shelf registration statement on Form S-3 with the Securities and Exchange Commission (SEC) for an indeterminate amount of securities, which became immediately effective. The shelf registration statement provides the Corporation with the ability to raise capital, subject to SEC rules and limitations, if the board of directors of the Corporation decides to do so. As previously discussed, the Corporation completed an $80.5 million public stock offering during the second quarter of 2014, which does not take into account the underwriting discount and issuance related expenses.
	The Corporation had previously filed a universal shelf registration statement with the SEC on May 23, 2013, which became effective on June 7, 2013, to register up to $100 million in securities. The Corporation's September 2013 common stock offering was completed under this universal shelf registration statement. Prior to filing its automatic shelf registration statement on June 12, 2014, the Corporation filed a post-effective amendment to terminate the effectiveness of the universal shelf registration statement and remove from registration all of the remaining securities covered by the universal shelf registration statement.
	Preferred Stock
	On April 20, 2009, the shareholders of the Corporation authorized the board of directors of the Corporation to issue up to 200,000 shares of preferred stock in connection with either an acquisition by the Corporation of an entity that has shares of preferred stock issued and outstanding pursuant to any program established by the United States government or participation by the Corporation in any program established by the United States government. At September 30, 2014, no shares of preferred stock were issued and outstanding.
	Legal Matters
	The Corporation and Chemical Bank are subject to certain legal actions arising in the ordinary course of business. In the opinion of management, after consultation with legal counsel, the ultimate disposition of these matters is not expected to have a material adverse effect on the consolidated financial condition or results of operations of the Corporation.
	Adopted Accounting Pronouncements
	Joint and Several Liability Arrangements
	In February 2013, the Financial Accounting Standards Board (FASB) issued ASU 2013-04, Liabilities (Topic 405): Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation is Fixed at the Reporting Date (ASU 2013-04). ASU 2013-04 provides guidance in relation to the recognition, measurement and disclosure of obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date. ASU 2013-04 is effective for interim and annual periods beginning after December 15, 2013 and should be applied retrospectively for all periods presented for those obligations resulting from joint and several liability arrangements that exist at the beginning of the fiscal year of adoption. The adoption of ASU 2013-04 as of January 1, 2014 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
	Accounting for Investments in Qualified Affordable Housing Projects
	In January 2014, the FASB issued ASU 2014-01, Investments—Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Qualified Affordable Housing Projects, a consensus of the FASB Emerging Issues Task Force (ASU 2014-01). ASU 2014-01 allows limited liability investors in qualified affordable housing projects to amortize the cost of their investment in proportion to tax credits and other tax benefits received (referred to as the "proportional amortization method"), and present the amortization as a component of income tax expense, as compared to the equity method, which requires the investment performance to be included in pre-tax income. The following conditions must be met in order for an investor to use the proportional amortization method: (i) it is probable that the tax credits allocable to the investor will be available, (ii) the investor does not have the ability to exercise significant influence over the operating and financial policies of the limited liability entity, (iii) substantially all of the projected benefits are from tax credits and other tax benefits, (iv) the investor's projected yield based solely on the cash flows from the tax credits and other tax benefits is positive, and (v) the investor is a limited liability investor in the limited liability entity for both legal and tax purposes, and the investor's liability is limited to its capital investment. The decision to apply the proportional amortization method is an accounting policy method that, if elected, must be applied consistently to all investments that meet the above conditions. An investor that does not qualify for the proportional amortization method or elects not to apply it will account for its investment under the cost or equity method in accordance with current guidance. ASU 2014-01 also introduces disclosure requirements for all investments in qualified affordable housing projects, regardless of the accounting method used for those investments. An investor must disclose (i) the nature of investments in qualified affordable housing projects and (ii) the effect of the measurement of those investments and the related tax credits on its financial statements. ASU 2014-01 is effective for public companies for interim and annual periods beginning after December 15, 2014, with early adoption permitted. Once adopted, the guidance must be applied retrospectively to all periods presented.
	The Corporation elected to early-adopt ASU 2014-01 as of January 1, 2014. The Corporation previously accounted for its investments in qualified affordable housing projects under the equity method; however, the Corporation determined that its investments in its qualified affordable housing projects meet the conditions set forth in ASU 2014-01 to account for these investments under the proportional amortization method. The Corporation invests in qualified affordable housing projects solely for the purpose of obtaining tax credits and other tax benefits. Accordingly, the Corporation believes that amortizing its investments in qualified affordable housing projects as a component of income tax expense rather than as a component of operating expenses better reflects the nature and intent of these investments. As a result of adopting ASU 2014-01, the Corporation recognized additional income tax expense attributable to the amortization of investments in qualified affordable housing projects of $0.1 million and $0.3 million during the three and nine months ended September 30, 2014, respectively. While the adoption of ASU 2014-01 requires retrospective application to all periods presented, the Corporation did not restate income tax expense for the three and nine months ended September 30, 2013 as the amount of additional income tax expense attributable to the amortization of investments in qualified affordable housing projects was not considered material. The Corporation's remaining investment in qualified affordable housing projects totaled $3.0 million at September 30, 2014, $3.2 million at December 31, 2013 and $3.3 million at September 30, 2013.
	Pending Accounting Pronouncements
In-Substance Foreclosures
In January 2014, the FASB issued ASU 2014-04, Receivables—Troubled Debt Restructurings by Creditors (Subtopic 310-40): Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure, a consensus of the FASB Emerging Issues Task Force (ASU 2014-04). ASU 2014-04 clarifies that an in-substance foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (i) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (ii) the borrower conveying all interest in the residential real estate property to the creditor to satisfy the loan through completion of a deed in lieu of foreclosure or similar legal agreement. ASU 2014-04 also requires disclosure of both the amount of foreclosed residential real estate property held by the creditor and the recorded investment in loans collateralized by residential real estate property that are in the process of foreclosure. ASU 2014-04 is effective for public companies for interim and annual periods beginning after December 15, 2014, with early adoption permitted. Once adopted, an entity can elect either (i) a modified retrospective transition method or (ii) a prospective transition method. The modified retrospective transition method is applied by means of a cumulative-effect adjustment to residential mortgage loans and foreclosed residential real estate properties existing as of the beginning of the period for which the amendments of ASU 2014-04 are effective, with real estate reclassified to loans measured at the carrying value of the real estate at the date of adoption and loans reclassified to real estate measured at the lower of net carrying value of the loan or the fair value of the real estate less costs to sell at the date of adoption. The prospective transition method is applied by means of applying the amendments of ASU 2014-04 to all instances of receiving physical possession of residential real estate properties that occur after the date of adoption. The adoption of ASU 2014-04 is not expected to have a material impact on the Corporation's consolidated financial condition or results of operations.
Share-Based Compensation
In June 2014, the FASB issued ASU 2014-12, Compensation—Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period, a consensus of the FASB Emerging Issues Task Force (ASU 2014-12). ASU 2014-12 requires that a performance target that affects vesting of share-based payment awards and that could be achieved after the requisite service period be treated as a performance condition. Compensation cost should be recognized in the period in which it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the periods for which the requisite service has already been rendered. If the performance target becomes probable of being achieved before the end of the requisite service period, the remaining unrecognized compensation cost should be recognized prospectively over the remaining requisite service period. The total amount of compensation cost recognized during and after the requisite service period should reflect the number of awards that are expected to vest and should be adjusted to reflect those awards that ultimately vest. The requisite service period ends when the employee can cease rendering service and still be eligible to vest in the award if the performance target is achieved. ASU 2014-12 is effective for all entities for interim and annual periods beginning after December 15, 2015, with early adoption permitted. An entity may apply the amendments in ASU 2014-12 either (i) prospectively to all awards granted or modified after the effective date or (ii) retrospectively to all awards with performance targets that are outstanding as of the beginning of the earliest annual period presented in the financial statements and to all new or modified awards thereafter. The adoption of ASU 2014-12 is not expected to have a material impact on the Corporation's consolidated financial condition or results of operations.
Government-Guaranteed Mortgage Loans
In August 2014, the FASB issued ASU 2014-14, Receivables—Troubled Debt Restructurings by Creditors (Subtopic 310-40): Classification of Certain Government Guaranteed Mortgage Loans upon Foreclosure, a consensus of the FASB Emerging Issues Task Force (ASU 2014-14). ASU 2014-14 provides clarifying guidance related to how creditors classify government-guaranteed loans upon foreclosure. Upon foreclosure of a government-guaranteed mortgage loan, the loan should be derecognized and a separate other receivable should be recognized if the following conditions are met: (i) the loan has a government guarantee that is not separable from the loan before foreclosure; (ii) at the time of foreclosure, the creditor has the intent to convey the real estate property to the guarantor and make a claim on the guarantee, and the creditor has the ability to recover under that claim; and (iii) at the time of foreclosure, any amount of the claim that is determined on the basis of the fair value of the real estate is fixed. The separate other receivable should be measured based on the amount of the loan balance (principal and interest) expected to be recovered from the guarantor at the time of foreclosure. ASU 2014-14 is effective for public companies for interim and annual periods beginning after December 15, 2014. An entity should adopt using either the modified retrospective method or the prospective transition method. An entity must apply the same method elected under ASU 2014-04. Early adoption is permitted if the entity has already adopted ASU 2014-04. The adoption of ASU 2014-14 is not expected to have a material impact on the Corporation's consolidated financial condition or results of operations.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Acquisitions	'
	Acquisitions
	Pending Acquisition of Northwestern Bancorp, Inc.
	On March 10, 2014, the Corporation and Northwestern Bancorp, Inc. (Northwestern), the parent company of Northwestern Bank, a community bank based in Traverse City, Michigan, entered into a definitive agreement whereby the Corporation will acquire Northwestern in an all cash transaction valued at $120 million, subject to adjustment under limited circumstances. The Corporation anticipates the transaction, with cost savings fully phased in and excluding the impact of nonrecurring transaction-related expenses, to be immediately accretive to earnings per share. Regulatory approval for the transaction was received on September 30, 2014 and the transaction is expected to close on October 31, 2014, subject to customary closing conditions. The Corporation recognized $1.3 million and $2.2 million of pre-tax nonrecurring transaction-related expenses during the three and nine months ended September 30, 2014, respectively.
	Acquisition of 21 Branches
	On December 7, 2012, Chemical Bank acquired 21 branches located in the Northeast and Battle Creek regions of Michigan, including $404 million in deposits and $44 million in loans (branch acquisition transaction). The purchase price of the branch offices, including equipment, was $8.1 million and the Corporation paid a premium on deposits of $11.5 million, or approximately 2.85% of total deposits. The loans were purchased at a discount of 1.75%. In connection with the branch acquisition transaction, the Corporation recorded goodwill of $6.8 million and other intangible assets attributable to customer core deposits of $5.6 million.
	Acquisition of O.A.K. Financial Corporation (OAK)
	On April 30, 2010, the Corporation acquired OAK and OAK's wholly-owned bank subsidiary, Byron Bank, for total consideration of $83.7 million. Byron Bank, which was subsequently consolidated with and into Chemical Bank, provided traditional banking services and products through 14 banking offices serving communities in Ottawa, Allegan and Kent counties in west Michigan. At the acquisition date, OAK had total assets of $820 million, including total loans of $627 million, and total deposits of $693 million, including brokered deposits of $193 million.
	Upon acquisition, the OAK loan portfolio had contractually required principal payments receivable of $683 million and a fair value of $627 million. The outstanding contractual principal balance and the carrying amount of the acquired loan portfolio were $286 million and $263 million, respectively, at September 30, 2014, compared to $320 million and $295 million, respectively, at December 31, 2013 and $334 million and $309 million, respectively, at September 30, 2013.
	Activity for the accretable yield, which includes contractually due interest for acquired loans that have been renewed or extended since the date of acquisition and continue to be accounted for in loan pools in accordance with ASC 310-30, follows:
			Nine Months Ended
			September 30,
			2014			2013
			(In thousands)
	Balance at beginning of period		$	32,610		$	49,390
	Additions (reductions)*		4,493			(997		)
	Accretion recognized in interest income		(11,262		)	(13,235		)
	Reclassification from nonaccretable difference		10,000			125
	Balance at end of period		$	35,841		$	35,283
	*	Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.
	As part of its ongoing assessment of the acquired loan portfolio, management has determined that the overall credit quality of the acquired loan portfolio has improved, which has resulted in an improvement in expected cash flows of loan pools in the acquired commercial loan portfolio. Accordingly, management reclassified $10.0 million during the first quarter of 2014 from the nonaccretable difference to the accretable yield for these acquired commercial loan pools, which will increase amounts recognized into interest income over the estimated remaining lives of these loan pools.

Investment_Securities

Investment Securities	9 Months Ended
	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]	'
Investment Securities	'
	Investment Securities
	The following is a summary of the amortized cost and fair value of investment securities available-for-sale and investment securities held-to-maturity at September 30, 2014, December 31, 2013 and September 30, 2013:
		Investment Securities Available-for-Sale
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	30-Sep-14
	Government sponsored agencies	$	76,626	$	354	$	42	$	76,938
	State and political subdivisions	39,589		1,375		—		40,964
	Residential mortgage-backed securities	252,908		846		2,715		251,039
	Collateralized mortgage obligations	141,273		346		1,174		140,445
	Corporate bonds	64,955		295		67		65,183
	Preferred stock	1,389		253		—		1,642
	Total	$	576,740	$	3,469	$	3,998	$	576,211
	31-Dec-13
	Government sponsored agencies	$	93,895	$	250	$	382	$	93,763
	State and political subdivisions	42,450		1,355		7		43,798
	Residential mortgage-backed securities	303,495		968		5,097		299,366
	Collateralized mortgage obligations	182,128		452		1,639		180,941
	Corporate bonds	65,028		499		252		65,275
	Preferred stock	1,389		63		25		1,427
	Total	$	688,385	$	3,587	$	7,402	$	684,570
	30-Sep-13
	Government sponsored agencies	$	86,065	$	264	$	404	$	85,925
	State and political subdivisions	44,191		1,386		5		45,572
	Residential mortgage-backed securities	310,550		1,144		3,534		308,160
	Collateralized mortgage obligations	200,407		199		2,148		198,458
	Corporate bonds	65,053		583		202		65,434
	Preferred stock	1,389		208		—		1,597
	Total	$	707,655	$	3,784	$	6,293	$	705,146
		Investment Securities Held-to-Maturity
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	30-Sep-14
	State and political subdivisions	$	308,062	$	5,704	$	6,476	$	307,290
	Trust preferred securities	10,500		—		3,515		6,985
	Total	$	318,562	$	5,704	$	9,991	$	314,275
	31-Dec-13
	State and political subdivisions	$	263,405	$	5,462	$	6,846	$	262,021
	Trust preferred securities	10,500		—		4,250		6,250
	Total	$	273,905	$	5,462	$	11,096	$	268,271
	30-Sep-13
	State and political subdivisions	$	272,079	$	5,978	$	8,441	$	269,616
	Trust preferred securities	10,500		—		4,250		6,250
	Total	$	282,579	$	5,978	$	12,691	$	275,866
	The majority of the Corporation’s residential mortgage-backed securities and collateralized mortgage obligations are backed by a U.S. government agency (Government National Mortgage Association) or a government sponsored enterprise (Federal Home Loan Mortgage Corporation or Federal National Mortgage Association).
	At September 30, 2014, the Corporation held $10.5 million of trust preferred investment securities that were recorded as held-to-maturity, with $10.0 million of these securities representing a 100% interest in a trust preferred investment security of a small non-public bank holding company in Michigan that has been assessed by the Corporation as financially strong. The remaining $0.5 million represents a 10% interest in another trust preferred investment security of a small non-public bank holding company located in Michigan that was categorized as well-capitalized under regulatory guidelines at September 30, 2014.
	At September 30, 2014, it was the Corporation’s opinion that the market for trust preferred investment securities was not active, and thus, in accordance with GAAP, when there is a significant decrease in the volume and activity for an asset or liability in relation to normal market activity, adjustments to transaction or quoted prices may be necessary or a change in valuation technique or multiple valuation techniques may be appropriate. The Corporation obtained pricing information for its trust preferred investment securities from an independent third-party pricing source. The pricing information was based on both observable inputs and unobservable inputs, including appropriate risk adjustments that market participants would make for possible nonperformance, illiquidity and issuer specifics such as size, leverage position and location. The observable inputs were based on the existing market and insight into appropriate rate of return adjustments that market participants would require for the additional risk associated with a single issue investment security of this nature. Based on the information obtained from the independent third-party pricing source, the Corporation calculated a fair value at September 30, 2014 of $6.7 million on its $10.0 million trust preferred investment security and $0.3 million on its $0.5 million trust preferred investment security, resulting in a combined unrealized loss of $3.5 million at that date.
	The following is a summary of the amortized cost and fair value of investment securities at September 30, 2014, by maturity, for both available-for-sale and held-to-maturity investment securities. The maturities of residential mortgage-backed securities and collateralized mortgage obligations are based on scheduled principal payments. The maturities of all other debt securities are based on final contractual maturity.
		30-Sep-14
		Amortized		Fair Value
		Cost
		(In thousands)
	Investment Securities Available-for-Sale:
	Due in one year or less	$	153,539	$	153,302
	Due after one year through five years	349,258		348,952
	Due after five years through ten years	68,701		68,537
	Due after ten years	3,853		3,778
	Preferred stock	1,389		1,642
	Total	$	576,740	$	576,211
	Investment Securities Held-to-Maturity:
	Due in one year or less	$	34,833	$	34,898
Due after one year through five years	135,150		136,359
Due after five years through ten years	95,222		95,839
Due after ten years	53,357		47,179
Total	$	318,562	$	314,275
The following schedule summarizes information for both available-for-sale and held-to-maturity investment securities with gross unrealized losses at September 30, 2014, December 31, 2013 and September 30, 2013, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position.
	Less Than 12 Months				12 Months or More				Total
	Fair		Gross		Fair		Gross		Fair		Gross
	Value		Unrealized		Value		Unrealized		Value		Unrealized
			Losses				Losses				Losses
	(In thousands)
30-Sep-14
Government sponsored agencies	$	1,744	$	4	$	24,810	$	38	$	26,554	$	42
State and political subdivisions	91,532		4,010		70,116		2,466		161,648		6,476
Residential mortgage-backed securities	34,280		144		196,045		2,571		230,325		2,715
Collateralized mortgage obligations	44,195		81		28,544		1,093		72,739		1,174
Corporate bonds	4,996		4		14,937		63		19,933		67
Trust preferred securities	—		—		6,985		3,515		6,985		3,515
Total	$	176,747	$	4,243	$	341,437	$	9,746	$	518,184	$	13,989
31-Dec-13
Government sponsored agencies	$	47,352	$	205	$	14,031	$	177	$	61,383	$	382
State and political subdivisions	126,345		6,475		19,074		378		145,419		6,853
Residential mortgage-backed securities	274,076		5,097		—		—		274,076		5,097
Collateralized mortgage obligations	84,995		1,127		14,684		512		99,679		1,639
Corporate bonds	14,931		78		19,826		174		34,757		252
Trust preferred securities	—		—		6,250		4,250		6,250		4,250
Preferred stock	1,024		25		—		—		1,024		25
Total	$	548,723	$	13,007	$	73,865	$	5,491	$	622,588	$	18,498
30-Sep-13
Government sponsored agencies	$	43,816	$	223	$	14,395	$	181	$	58,211	$	404
State and political subdivisions	120,232		6,918		30,915		1,528		151,147		8,446
Residential mortgage-backed securities	267,495		3,532		40		2		267,535		3,534
Collateralized mortgage obligations	129,049		1,617		15,302		531		144,351		2,148
Corporate bonds	9,926		85		19,883		117		29,809		202
Trust preferred securities	—		—		6,250		4,250		6,250		4,250
Total	$	570,518	$	12,375	$	86,785	$	6,609	$	657,303	$	18,984
An assessment is performed quarterly by the Corporation to determine whether unrealized losses in its investment securities portfolio are temporary or other-than-temporary by carefully considering all available information. The Corporation reviews factors such as financial statements, credit ratings, news releases and other pertinent information of the underlying issuer or company to make its determination. Management did not believe any individual unrealized loss on any investment security, as of September 30, 2014, represented an other-than-temporary impairment (OTTI). Management believed that the unrealized losses on investment securities at September 30, 2014 were temporary in nature and due primarily to changes in interest rates and reduced market liquidity and not as a result of credit-related issues. Unrealized losses of $3.5 million in the trust preferred securities portfolio, related to trust preferred securities of two well-capitalized bank holding companies in Michigan, were attributable to illiquidity in financial markets for these types of investments. The Corporation performed an analysis of the creditworthiness of these issuers and concluded that, at September 30, 2014, the Corporation expected to recover the entire amortized cost basis of these investment securities.
At September 30, 2014, the Corporation did not have the intent to sell any of its impaired investment securities and believed that it was more-likely-than-not that the Corporation will not have to sell any such investment securities before a full recovery of amortized cost. Accordingly, at September 30, 2014, the Corporation believed the impairments in its investment securities portfolio were temporary in nature. However, there is no assurance that OTTI may not occur in the future.

Loans

Loans	9 Months Ended
	Sep. 30, 2014
Receivables [Abstract]	'
Loans	'
	Loans
	Loan portfolio segments are defined as the level at which an entity develops and documents a systematic methodology to determine its allowance. The Corporation has two loan portfolio segments (commercial loans and consumer loans) that it uses in determining the allowance. Both quantitative and qualitative factors are used by management at the loan portfolio segment level in determining the adequacy of the allowance for the Corporation. Classes of loans are a disaggregation of an entity’s loan portfolio segments. Classes of loans are defined as a group of loans which share similar initial measurement attributes, risk characteristics, and methods for monitoring and assessing credit risk. The Corporation has seven classes of loans, which are set forth below.
	Commercial — Loans and lines of credit to varying types of businesses, including municipalities, school districts and nonprofit organizations, for the purpose of supporting working capital, operational needs and term financing of equipment. Repayment of such loans is generally provided through operating cash flows of the business. Commercial loans are predominately secured by equipment, inventory, accounts receivable, personal guarantees of the owner and other sources of repayment, although the Corporation may also secure commercial loans with real estate.
	Commercial real estate — Loans secured by real estate occupied by the borrower for ongoing operations, non-owner occupied real estate leased to one or more tenants and vacant land that has been acquired for investment or future land development.
	Real estate construction — Secured loans for the construction of business properties. Real estate construction loans often convert to a commercial real estate loan at the completion of the construction period.
	Land development — Secured development loans made to borrowers for the purpose of infrastructure improvements to vacant land to create finished marketable residential and commercial lots/land. Most land development loans are originated with the intention that the loans will be paid through the sale of developed lots/land by the developers within twelve months of the completion date. Land development loans at September 30, 2014, December 31, 2013 and September 30, 2013 were primarily comprised of loans to develop residential properties.
	Residential mortgage — Loans secured by one- to four-family residential properties, generally with fixed interest rates for periods of fifteen years or less. The loan-to-value ratio at the time of origination is generally 80% or less. Residential mortgage loans with a loan-to-value ratio of more than 80% generally require private mortgage insurance.
	Consumer installment — Loans to consumers primarily for the purpose of acquiring automobiles, recreational vehicles and personal watercraft. These loans consist of relatively small amounts that are spread across many individual borrowers.
	Home equity — Loans and lines of credit whereby consumers utilize equity in their personal residence, generally through a second mortgage, as collateral to secure the loan.
	Commercial, commercial real estate, real estate construction and land development loans are referred to as the Corporation’s commercial loan portfolio, while residential mortgage, consumer installment and home equity loans are referred to as the Corporation’s consumer loan portfolio. A summary of loans follows:
			September 30,				December 31,				September 30,
			2014				2013				2013
			(In thousands)
	Commercial loan portfolio:
	Commercial		$	1,239,946			$	1,176,307			$	1,128,122
	Commercial real estate		1,322,646				1,232,658				1,215,631
	Real estate construction		125,782				89,795				78,361
	Land development		10,434				20,066				23,673
	Subtotal		2,698,808				2,518,826				2,445,787
	Consumer loan portfolio:
	Residential mortgage		984,049				960,423				942,777
	Consumer installment		783,443				644,769				622,040
	Home equity		574,620				523,603				512,067
	Subtotal		2,342,112				2,128,795				2,076,884
	Total loans		$	5,040,920			$	4,647,621			$	4,522,671
	Credit Quality Monitoring
	The Corporation maintains loan policies and credit underwriting standards as part of the process of managing credit risk. These standards include making loans generally only within the Corporation’s market areas. The Corporation’s lending markets generally consist of communities across the lower peninsula of Michigan, except for the southeastern portion of Michigan. The Corporation has no foreign loans.
	The Corporation has a commercial loan portfolio approval process involving underwriting and individual and group loan approval authorities to consider credit quality and loss exposure at loan origination. The loans in the Corporation’s commercial loan portfolio are risk rated at origination based on the grading system set forth below. The approval authority of relationship managers is established based on experience levels, with credit decisions greater than $1.0 million requiring group loan authority approval, except for four executive and senior officers who have varying limits exceeding $1.5 million and up to $3.5 million. With respect to the group loan authorities, the Corporation has a loan committee, consisting of certain executive and senior officers, that meets weekly to consider loans ranging in amounts from $1.0 million to $5.0 million, depending on risk rating and credit action required. A directors’ loan committee, consisting of nine members of the board of directors, including the chief executive officer and senior credit officer, meets bi-weekly to consider loans in amounts over $5.0 million, and certain loans under $5.0 million depending on a loan’s risk rating and credit action required. Loans over $10.0 million require majority approval of the board of directors.
	The majority of the Corporation’s consumer loan portfolio is comprised of secured loans that are relatively small. The Corporation’s consumer loan portfolio has a centralized approval process which utilizes standardized underwriting criteria. The ongoing measurement of credit quality of the consumer loan portfolio is largely done on an exception basis. If payments are made on schedule, as agreed, then no further monitoring is performed. However, if delinquency occurs, the delinquent loans are turned over to the Corporation’s collection department for resolution, resulting in repossession or foreclosure if payments are not brought current. Credit quality for the entire consumer loan portfolio is measured by the periodic delinquency rate, nonaccrual amounts and actual losses incurred.
	Loans in the commercial loan portfolio tend to be larger and more complex than those in the consumer loan portfolio, and therefore, are subject to more intensive monitoring. All loans in the commercial loan portfolio have an assigned relationship manager, and most borrowers provide periodic financial and operating information that allows the relationship managers to stay abreast of credit quality during the life of the loans. The risk ratings of loans in the commercial loan portfolio are reassessed at least annually, with loans below an acceptable risk rating reassessed more frequently and reviewed by various loan committees within the Corporation at least quarterly.
	The Corporation maintains a centralized independent loan review function that monitors the approval process and ongoing asset quality of the loan portfolio, including the accuracy of loan grades. The Corporation also maintains an independent appraisal review function that participates in the review of all appraisals obtained by the Corporation for loans in the commercial loan portfolio.
	Credit Quality Indicators
	Commercial Loan Portfolio
	The Corporation uses a nine grade risk rating system to monitor the ongoing credit quality of its commercial loan portfolio. These loan grades rank the credit quality of a borrower by measuring liquidity, debt capacity, coverage and payment behavior as shown in the borrower’s financial statements. The loan grades also measure the quality of the borrower’s management and the repayment support offered by any guarantors. A summary of the Corporation’s loan grades (or characteristics of the loans within each grade) follows:
	Risk Grades 1-5 (Acceptable Credit Quality) — All loans in risk grades 1 through 5 are considered to be acceptable credit risks by the Corporation and are grouped for purposes of allowance for loan loss considerations and financial reporting. The five grades essentially represent a ranking of loans that are all viewed to be of acceptable credit quality, taking into consideration the various factors mentioned above, but with varying degrees of financial strength, debt coverage, management and factors that could impact credit quality. Business credits within risk grades 1 through 5 range from Risk Grade 1: Prime Quality (factors include: excellent business credit; excellent debt capacity and coverage; outstanding management; strong guarantors; superior liquidity and net worth; favorable loan-to-value ratios; debt secured by cash or equivalents, or backed by the full faith and credit of the U.S. Government) to Risk Grade 5: Acceptable Quality With Care (factors include: acceptable business credit, but with added risk due to specific industry or internal situations).
	Risk Grade 6 (Watch) — A business credit that is not acceptable within the Corporation’s loan origination criteria; cash flow may not be adequate or is continually inconsistent to service current debt; financial condition has deteriorated as company trends/management have become inconsistent; the company is slow in furnishing quality financial information; working capital needs of the company are reliant on short-term borrowings; personal guarantees are weak and/or with little or no liquidity; the net worth of the company has deteriorated after recent or continued losses; the loan requires constant monitoring and attention from the Corporation; payment delinquencies becoming more serious; if left uncorrected, these potential weaknesses may, at some future date, result in deterioration of repayment prospects.
	Risk Grade 7 (Substandard — Accrual) — A business credit that is inadequately protected by the current financial net worth and paying capacity of the obligor or of the collateral pledged, if any; management has deteriorated or has become non-existent; quality financial information is not available; a high level of maintenance is required by the Corporation; cash flow can no longer support debt requirements; loan payments are continually and/or severely delinquent; negative net worth; personal guaranty has become insignificant; a credit that has a well-defined weakness or weaknesses that jeopardize the liquidation of the debt. The Corporation still expects a full recovery of all contractual principal and interest payments; however, a possibility exists that the Corporation will sustain some loss if deficiencies are not corrected.
	Risk Grade 8 (Substandard — Nonaccrual) — A business credit accounted for on a nonaccrual basis that has all the weaknesses inherent in a loan classified as risk grade 7 with the added characteristic that the weaknesses are so pronounced that, on the basis of current financial information, conditions, and values, collection in full is highly questionable; a partial loss is possible and interest is no longer being accrued. This loan meets the definition of an impaired loan. The risk of loss requires analysis to determine whether a valuation allowance needs to be established.
	Risk Grade 9 (Substandard — Doubtful) — A business credit that has all the weaknesses inherent in a loan classified as risk grade 8 and interest is no longer being accrued, but additional deficiencies make it highly probable that liquidation will not satisfy the majority of the obligation; the primary source of repayment is nonexistent and there is doubt as to the value of the secondary source of repayment; the possibility of loss is likely, but current pending factors could strengthen the credit. This loan meets the definition of an impaired loan. A loan charge-off is recorded when management deems an amount uncollectible; however, the Corporation will establish a valuation allowance for probable losses, if required.
	The Corporation considers all loans graded 1 through 5 as acceptable credit risks and structures and manages such relationships accordingly. Periodic financial and operating data combined with regular loan officer interactions are deemed adequate to monitor borrower performance. Loans graded 6 and 7 are considered higher-risk credits than loans graded 1 through 5 and the frequency of loan officer contact and receipt of financial data is increased to stay abreast of borrower performance. Loans graded 8 and 9 are considered problematic and require special care. Further, loans graded 6 through 9 are managed and monitored regularly through a number of processes, procedures and committees, including oversight by a loan administration committee comprised of executive and senior management of the Corporation, which include highly structured reporting of financial and operating data, intensive loan officer intervention and strategies to exit, as well as potential management by the Corporation’s special assets group.
	The following schedule presents the recorded investment of loans in the commercial loan portfolio by risk rating categories at September 30, 2014, December 31, 2013 and September 30, 2013:
			Commercial				Commercial Real Estate				Real Estate				Land			Total
											Construction				Development
			(In thousands)
	30-Sep-14
	Originated Portfolio:
	Risk Grades 1-5		$	1,098,885			$	1,090,397			$	110,402			$	3,228		$	2,302,912
	Risk Grade 6		16,469				27,087				666				943			45,165
	Risk Grade 7		34,409				42,134				3,751				618			80,912
	Risk Grade 8		18,006				23,847				162				1,467			43,482
	Risk Grade 9		207				11				—				—			218
	Subtotal		1,167,976				1,183,476				114,981				6,256			2,472,689
	Acquired Portfolio:
	Risk Grades 1-5		58,342				130,887				10,801				2,303			202,333
	Risk Grade 6		3,909				2,086				—				—			5,995
	Risk Grade 7		5,885				6,197				—				148			12,230
	Risk Grade 8		3,834				—				—				1,727			5,561
	Risk Grade 9		—				—				—				—			—
	Subtotal		71,970				139,170				10,801				4,178			226,119
	Total		$	1,239,946			$	1,322,646			$	125,782			$	10,434		$	2,698,808
	31-Dec-13
	Originated Portfolio:
	Risk Grades 1-5		$	1,024,461			$	991,964			$	75,696			$	6,874		$	2,098,995
Risk Grade 6		20,082				34,248				654				969			55,953
Risk Grade 7		29,776				30,377				738				3,128			64,019
Risk Grade 8		17,414				28,580				371				2,309			48,674
Risk Grade 9		960				18				—				—			978
Subtotal		1,092,693				1,085,187				77,459				13,280			2,268,619
Acquired Portfolio:
Risk Grades 1-5		73,763				133,653				12,336				4,667			224,419
Risk Grade 6		5,472				5,022				—				—			10,494
Risk Grade 7		852				7,792				—				—			8,644
Risk Grade 8		3,527				1,004				—				2,119			6,650
Risk Grade 9		—				—				—				—			—
Subtotal		83,614				147,471				12,336				6,786			250,207
Total		$	1,176,307			$	1,232,658			$	89,795			$	20,066		$	2,518,826
30-Sep-13
Originated Portfolio:
Risk Grades 1-5		$	974,903			$	963,394			$	64,210			$	7,760		$	2,010,267
Risk Grade 6		16,439				37,572				58				1,063			55,132
Risk Grade 7		37,644				30,969				1,337				4,870			74,820
Risk Grade 8		9,753				28,186				183				2,954			41,076
Risk Grade 9		2,056				437				—				—			2,493
Subtotal		1,040,795				1,060,558				65,788				16,647			2,183,788
Acquired Portfolio:
Risk Grades 1-5		82,648				141,234				12,573				4,604			241,059
Risk Grade 6		2,620				4,837				—				—			7,457
Risk Grade 7		992				7,847				—				—			8,839
Risk Grade 8		1,067				1,155				—				2,422			4,644
Risk Grade 9		—				—				—				—			—
Subtotal		87,327				155,073				12,573				7,026			261,999
Total		$	1,128,122			$	1,215,631			$	78,361			$	23,673		$	2,445,787
Consumer Loan Portfolio
The Corporation evaluates the credit quality of loans in the consumer loan portfolio based on the performing or nonperforming status of the loan. Loans in the consumer loan portfolio that are performing in accordance with original contractual terms and are less than 90 days past due and accruing interest are considered to be in a performing status, while those that are in nonaccrual status, contractually past due 90 days or more as to interest or principal payments or classified as a nonperforming TDR are considered to be in a nonperforming status. Nonaccrual TDRs in the consumer loan portfolio are included with nonaccrual loans, while other TDRs in the consumer loan portfolio are considered in a nonperforming status until they meet the Corporation’s definition of a performing TDR, at which time they are considered in a performing status.
The following schedule presents the recorded investment of loans in the consumer loan portfolio based on loans in a performing status and loans in a nonperforming status at September 30, 2014, December 31, 2013 and September 30, 2013:
		Residential Mortgage				Consumer				Home Equity				Total
						Installment								Consumer
		(In thousands)
30-Sep-14
Originated Loans:
Performing		$	963,469			$	782,087			$	544,227			$	2,289,783
Nonperforming		10,720				527				3,895				15,142
Subtotal		974,189				782,614				548,122				2,304,925
Acquired Loans:
Performing		9,658				728				26,327				36,713
Nonperforming		202				101				171				474
Subtotal		9,860				829				26,498				37,187
Total		$	984,049			$	783,443			$	574,620			$	2,342,112
31-Dec-13
Originated Loans:
Performing		$	934,747			$	642,370			$	488,996			$	2,066,113
Nonperforming		14,134				676				3,382				18,192
Subtotal		948,881				643,046				492,378				2,084,305
Acquired Loans:
Performing		11,481				1,723				31,182				44,386
Nonperforming		61				—				43				104
Subtotal		11,542				1,723				31,225				44,490
Total		$	960,423			$	644,769			$	523,603			$	2,128,795
30-Sep-13
Originated Loans:
Performing		$	918,931			$	619,346			$	475,439			$	2,013,716
Nonperforming		11,850				665				3,709				16,224
Subtotal		930,781				620,011				479,148				2,029,940
Acquired Loans:
Performing		11,918				2,029				32,737				46,684
Nonperforming		78				—				182				260
Subtotal		11,996				2,029				32,919				46,944
Total		$	942,777			$	622,040			$	512,067			$	2,076,884
Nonperforming Loans
A summary of nonperforming loans follows:
		September 30,				December 31,				September 30,
		2014				2013				2013
		(In thousands)
Nonaccrual loans:
Commercial		$	18,213			$	18,374			$	11,809
Commercial real estate		23,858				28,598				28,623
Real estate construction		162				371				183
Land development		1,467				2,309				2,954
Residential mortgage		6,693				8,921				8,029
Consumer installment		527				676				665
Home equity		2,116				2,648				3,023
Total nonaccrual loans		53,036				61,897				55,286
Accruing loans contractually past due 90 days or more as to interest or principal payments:
Commercial		16				536				281
Commercial real estate		87				190				—
Real estate construction		—				—				—
Land development		—				—				—
Residential mortgage		380				537				692
Consumer installment		—				—				—
Home equity		1,779				734				686
Total accruing loans contractually past due 90 days or more as to interest or principal payments		2,262				1,997				1,659
Nonperforming TDRs:
Commercial loan portfolio		11,797				13,414				15,744
Consumer loan portfolio		3,647				4,676				3,129
Total nonperforming TDRs		15,444				18,090				18,873
Total nonperforming loans		$	70,742			$	81,984			$	75,818
The Corporation’s nonaccrual loans at September 30, 2014, December 31, 2013 and September 30, 2013 included $40.5 million, $37.3 million and $39.1 million, respectively, of nonaccrual TDRs.
Impaired Loans
The following schedule presents impaired loans by classes of loans at September 30, 2014, December 31, 2013 and September 30, 2013:
		Recorded				Unpaid				Related
		Investment				Principal				Valuation
						Balance				Allowance
		(In thousands)
30-Sep-14
Impaired loans with a valuation allowance:
Commercial		$	1,253			$	1,396			$	313
Commercial real estate		3,779				4,094				862
Real estate construction		—				—				—
Land development		—				—				—
Residential mortgage		19,629				19,629				328
Subtotal		24,661				25,119				1,503
Impaired loans with no related valuation allowance:
Commercial		40,344				45,259				—
Commercial real estate		45,550				59,037				—
Real estate construction		162				369				—
Land development		3,244				5,969				—
Residential mortgage		6,693				6,693				—
Consumer installment		527				527				—
Home equity		2,116				2,116				—
Subtotal		98,636				119,970				—
Total impaired loans:
Commercial		41,597				46,655				313
Commercial real estate		49,329				63,131				862
Real estate construction		162				369				—
Land development		3,244				5,969				—
Residential mortgage		26,322				26,322				328
Consumer installment		527				527				—
Home equity		2,116				2,116				—
Total		$	123,297			$	145,089			$	1,503
31-Dec-13
Impaired loans with a valuation allowance:
Commercial		$	2,517			$	2,656			$	728
Commercial real estate		2,576				2,965				353
Real estate construction		—				—				—
Land development		—				—				—
Residential mortgage		17,408				17,408				510
Subtotal		22,501				23,029				1,591
Impaired loans with no related valuation allowance:
Commercial		38,838				44,377				—
Commercial real estate		48,220				61,444				—
Real estate construction		371				478				—
Land development		7,170				11,817				—
Residential mortgage		8,921				8,921				—
Consumer installment		676				676				—
Home equity		2,648				2,648				—
Subtotal		106,844				130,361				—
Total impaired loans:
Commercial		41,355				47,033				728
Commercial real estate		50,796				64,409				353
Real estate construction		371				478				—
Land development		7,170				11,817				—
Residential mortgage		26,329				26,329				510
Consumer installment		676				676				—
Home equity		2,648				2,648				—
Total		$	129,345			$	153,390			$	1,591
		Recorded				Unpaid				Related
		Investment				Principal				Valuation
						Balance				Allowance
		(In thousands)
30-Sep-13
Impaired loans with a valuation allowance:
Commercial		$	5,059			$	5,803			$	1,857
Commercial real estate		6,684				7,901				1,651
Real estate construction		183				253				33
Land development		517				653				97
Residential mortgage		17,731				17,731				585
Subtotal		30,174				32,341				4,223
Impaired loans with no related valuation allowance:
Commercial		21,543				25,642				—
Commercial real estate		43,178				57,256				—
Real estate construction		133				133				—
Land development		9,095				13,347				—
Residential mortgage		8,029				8,029				—
Consumer installment		665				665				—
Home equity		3,023				3,023				—
Subtotal		85,666				108,095				—
Total impaired loans:
Commercial		26,602				31,445				1,857
Commercial real estate		49,862				65,157				1,651
Real estate construction		316				386				33
Land development		9,612				14,000				97
Residential mortgage		25,760				25,760				585
Consumer installment		665				665				—
Home equity		3,023				3,023				—
Total		$	115,840			$	140,436			$	4,223
The difference between an impaired loan’s recorded investment and the unpaid principal balance for originated loans represents a partial charge-off resulting from a confirmed loss due to the value of the collateral securing the loan being below the loan balance and management’s assessment that full collection of the loan balance is not likely, and for acquired loans that meet the definition of an impaired loan represents fair value adjustments recognized at the acquisition date attributable to expected credit losses and the discounting of expected cash flows at market interest rates. The difference between the recorded investment and the unpaid principal balance of $21.8 million, $24.0 million and $24.6 million at September 30, 2014, December 31, 2013 and September 30, 2013, respectively, includes confirmed losses (partial charge-offs) of $18.2 million, $20.2 million and $21.2 million, respectively, and fair value discount adjustments of $3.6 million, $3.8 million and $3.4 million, respectively.
Impaired loans included $10.2 million, $9.8 million and $7.6 million at September 30, 2014, December 31, 2013 and September 30, 2013, respectively, of acquired loans that were not performing in accordance with original contractual terms. Acquired loans that are not performing in accordance with contractual terms are not reported as nonperforming loans because these loans are recorded in pools at their net realizable value based on the principal and interest the Corporation expects to collect on these loans. Impaired loans also included $44.6 million, $39.6 million and $34.1 million at September 30, 2014, December 31, 2013 and September 30, 2013, respectively, of performing TDRs.
The following schedule presents information related to impaired loans for the three and nine months ended September 30, 2014 and 2013:
		Three Months Ended September 30, 2014								Nine Months Ended September 30, 2014
		Average				Interest Income				Average				Interest Income
		Recorded				Recognized				Recorded				Recognized
		Investment				While on				Investment				While on
						Impaired Status								Impaired Status
		(In thousands)
Commercial		$	41,903			$	346			$	42,046			$	1,026
Commercial real estate		50,133				263				51,571				990
Real estate construction		162				—				164				—
Land development		3,284				30				4,079				101
Residential mortgage		26,166				310				26,561				941
Consumer installment		481				—				630				—
Home equity		2,246				—				2,212				—
Total		$	124,375			$	949			$	127,263			$	3,058
		Three Months Ended September 30, 2013								Nine Months Ended September 30, 2013
		Average				Interest Income				Average				Interest Income
		Recorded				Recognized				Recorded				Recognized
		Investment				While on				Investment				While on
						Impaired Status								Impaired Status
		(In thousands)
Commercial		$	27,025			$	215			$	26,894			$	633
Commercial real estate		50,266				284				53,482				984
Real estate construction		414				2				395				7
Land development		9,615				79				10,470				261
Residential mortgage		25,826				278				27,216				847
Consumer installment		632				—				666				—
Home equity		3,091				—				2,977				—
Total		$	116,869			$	858			$	122,100			$	2,732
The following schedule presents the aging status of the recorded investment in loans by classes of loans at September 30, 2014, December 31, 2013 and September 30, 2013:
		31-60				61-89				Accruing				Non-accrual			Total			Current		Total
		Days				Days				Loans				Loans			Past Due					Loans
		Past Due				Past Due				Past Due
										90 Days
										or More
		(In thousands)
30-Sep-14
Originated Portfolio:
Commercial		$	3,717			$	1,145			$	16			$	18,213		$	23,091		$	1,144,885	$	1,167,976
Commercial real estate		3,837				29				87				23,858			27,811			1,155,665		1,183,476
Real estate construction		1,075				—				—				162			1,237			113,744		114,981
Land development		—				—				—				1,467			1,467			4,789		6,256
Residential mortgage		1,669				—				380				6,693			8,742			965,447		974,189
Consumer installment		2,859				437				—				527			3,823			778,791		782,614
Home equity		2,592				361				1,779				2,116			6,848			541,274		548,122
Total		$	15,749			$	1,972			$	2,262			$	53,036		$	73,019		$	4,704,595	$	4,777,614
Acquired Portfolio:
Commercial		$	—			$	—			$	6,514			$	—		$	6,514		$	65,456	$	71,970
Commercial real estate		—				—				1,559				—			1,559			137,611		139,170
Real estate construction		—				—				—				—			—			10,801		10,801
Land development		—				—				1,727				—			1,727			2,451		4,178
Residential mortgage		—				—				202				—			202			9,658		9,860
Consumer installment		—				—				—				—			—			829		829
Home equity		335				—				227				—			562			25,936		26,498
Total		$	335			$	—			$	10,229			$	—		$	10,564		$	252,742	$	263,306
		31-60				61-89				Accruing				Non-accrual			Total			Current		Total
		Days				Days				Loans				Loans			Past Due					Loans
		Past Due				Past Due				Past Due
										90 Days
										or More
		(In thousands)
31-Dec-13
Originated Portfolio:
Commercial		$	4,748			$	865			$	536			$	18,374		$	24,523		$	1,068,170	$	1,092,693
Commercial real estate		8,560				1,604				190				28,598			38,952			1,046,235		1,085,187
Real estate construction		—				4,107				—				371			4,478			72,981		77,459
Land development		—				—				—				2,309			2,309			10,971		13,280
Residential mortgage		2,191				103				537				8,921			11,752			937,129		948,881
Consumer installment		2,630				359				—				676			3,665			639,381		643,046
Home equity		1,452				278				734				2,648			5,112			487,266		492,378
Total		$	19,581			$	7,316			$	1,997			$	61,897		$	90,791		$	4,262,133	$	4,352,924
Acquired Portfolio:
Commercial		$	—			$	—			$	5,656			$	—		$	5,656		$	77,958	$	83,614
Commercial real estate		—				133				1,695				—			1,828			145,643		147,471
Real estate construction		—				—				—				—			—			12,336		12,336
Land development		—				—				2,332				—			2,332			4,454		6,786
Residential mortgage		—				—				61				—			61			11,481		11,542
Consumer installment		3				51				—				—			54			1,669		1,723
Home equity		394				—				43				—			437			30,788		31,225
Total		$	397			$	184			$	9,787			$	—		$	10,368		$	284,329	$	294,697
30-Sep-13
Originated Portfolio:
Commercial		$	7,833			$	1,542			$	281			$	11,809		$	21,465		$	1,019,330	$	1,040,795
Commercial real estate		6,533				2,274				—				28,623			37,430			1,023,128		1,060,558
Real estate construction		90				5,385				—				183			5,658			60,130		65,788
Land development		187				—				—				2,954			3,141			13,506		16,647
Residential mortgage		1,739				76				692				8,029			10,536			920,245		930,781
Consumer installment		2,980				350				—				665			3,995			616,016		620,011
Home equity		2,344				434				686				3,023			6,487			472,661		479,148
Total		$	21,706			$	10,061			$	1,659			$	55,286		$	88,712		$	4,125,016	$	4,213,728
Acquired Portfolio:
Commercial		$	67			$	—			$	1,574			$	—		$	1,641		$	85,686	$	87,327
Commercial real estate		439				—				3,355				—			3,794			151,279		155,073
Real estate construction		—				—				—				—			—			12,573		12,573
Land development		—				—				2,422				—			2,422			4,604		7,026
Residential mortgage		264				—				77				—			341			11,655		11,996
Consumer installment		3				1				—				—			4			2,025		2,029
Home equity		389				79				182				—			650			32,269		32,919
Total		$	1,162			$	80			$	7,610			$	—		$	8,852		$	300,091	$	308,943
Loans Modified Under Troubled Debt Restructurings (TDRs)
The following schedule presents the Corporation’s loans reported as TDRs at September 30, 2014, December 31, 2013 and September 30, 2013:
		Performing TDRs				Non-Performing TDRs				Nonaccrual TDRs				Total
		(In thousands)
30-Sep-14
Commercial loan portfolio		$	28,606			$	11,797			$	36,549			$	76,952
Consumer loan portfolio		15,982				3,647				3,996				23,625
Total		$	44,588			$	15,444			$	40,545			$	100,577
31-Dec-13
Commercial loan portfolio		$	26,839			$	13,414			$	31,961			$	72,214
Consumer loan portfolio		12,732				4,676				5,321				22,729
Total		$	39,571			$	18,090			$	37,282			$	94,943
30-Sep-13
Commercial loan portfolio		$	19,469			$	15,744			$	34,124			$	69,337
Consumer loan portfolio		14,602				3,129				4,949				22,680
Total		$	34,071			$	18,873			$	39,073			$	92,017
The following schedule provides information on the Corporation's TDRs that were modified during the three and nine months ended September 30, 2014 and 2013:
	Three Months Ended September 30, 2014											Nine Months Ended September 30, 2014
	Number			Pre-				Post-				Number			Pre-			Post-
	of Loans			Modification				Modification				of Loans			Modification			Modification
				Recorded				Recorded							Recorded			Recorded
				Investment				Investment							Investment			Investment
	(Dollars in thousands)
Commercial loan portfolio:
Commercial	7			$	448			$	448			34			$	12,379		$	12,379
Commercial real estate	7			1,138				1,138				28			7,062			7,062
Land development	—			—				—				1			72			72
Subtotal – commercial loan portfolio	14			1,586				1,586				63			19,513			19,513
Consumer loan portfolio	14			572				565				107			3,208			3,191
Total	28			$	2,158			$	2,151			170			$	22,721		$	22,704
	Three Months Ended September 30, 2013 (As Revised)											Nine Months Ended September 30, 2013 (As Revised)
	Number			Pre-				Post-				Number			Pre-			Post-
	of Loans			Modification				Modification				of Loans			Modification			Modification
				Recorded				Recorded							Recorded			Recorded
				Investment				Investment							Investment			Investment
	(Dollars in thousands)
Commercial loan portfolio:
Commercial	6			$	716			$	716			25			$	5,075		$	5,075
Commercial real estate	8			3,924				3,924				32			11,587			11,587
Real estate construction	—			—				—				2			364			364
Land development	—			—				—				4			1,958			1,958
Subtotal – commercial loan portfolio	14			4,640				4,640				63			18,984			18,984
Consumer loan portfolio	23			1,773				1,730				60			3,929			3,830
Total	37			$	6,413			$	6,370			123			$	22,913		$	22,814
The pre-modification and post-modification recorded investment represents amounts as of the date of loan modification. The difference between the pre-modification and post-modification recorded investment of residential mortgage TDRs represents impairment recognized by the Corporation through the provision for loan losses computed based on a loan's post-modification present value of expected future cash flows discounted at the loan's original effective interest rate.
The following schedule includes TDRs for which there was a payment default during the three and nine months ended September 30, 2014 and 2013, whereby the borrower was past due with respect to principal and/or interest for 90 days or more, and the loan became a TDR during the twelve-month period prior to the default:
		Three Months Ended September 30, 2014							Nine Months Ended September 30, 2014
		Number of			Principal Balance at End of Period				Number of			Principal Balance at End of Period
		Loans							Loans
		(Dollars in thousands)
Commercial loan portfolio:
Commercial		—			$	—			6			$	875
Commercial real estate		—			—				5			2,273
Subtotal – commercial loan portfolio		—			—				11			3,148
Consumer loan portfolio		4			162				7			242
Total		4			$	162			18			$	3,390
		Three Months Ended September 30, 2013 (As Revised)							Nine Months Ended September 30, 2013 (As Revised)
		Number of			Principal Balance at End of Period				Number of			Principal Balance at End of Period
		Loans							Loans
		(Dollars in thousands)
Commercial loan portfolio:
Commercial		2			$	1,047			19			$	2,100
Commercial real estate		4			3,614				5			3,740
Real estate construction		—			—				1			160
Land development		—			—				2			1,526
Subtotal – commercial loan portfolio		6			4,661				27			7,526
Consumer loan portfolio		6			142				15			645
Total		12			$	4,803			42			$	8,171
During the three and nine months ended September 30, 2013, the Corporation had excluded nonaccrual TDRs from the schedule of TDRs that were modified during the three and nine months ended September 30, 2013 and the schedule of TDRs for which there was a payment default during the three and nine months ended September 30, 2013. The Corporation has revised the amounts reported for the three and nine months ended September 30, 2013 in these schedules to include activity related to all TDRs, including nonaccrual TDRs.
Allowance for Loan Losses
The following schedule presents, by loan portfolio segment, the changes in the allowance for the three and nine months ended September 30, 2014 and details regarding the balance in the allowance and the recorded investment in loans at September 30, 2014 by impairment evaluation method.
		Commercial				Consumer				Unallocated				Total
		Loan				Loan
		Portfolio				Portfolio
		(In thousands)
Changes in allowance for loan losses for the three months ended September 30, 2014:
Beginning balance		$	44,224			$	29,565			$	4,004			$	77,793
Provision for loan losses		715				834				(49		)		1,500
Charge-offs		(1,733		)		(1,889		)		—				(3,622		)
Recoveries		789				546				—				1,335
Ending balance		$	43,995			$	29,056			$	3,955			$	77,006
Changes in allowance for loan losses for the nine months ended September 30, 2014:
Beginning balance		$	44,482			$	30,145			$	4,445			$	79,072
Provision for loan losses		2,114				2,976				(490		)		4,600
Charge-offs		(4,756		)		(5,713		)		—				(10,469		)
Recoveries		2,155				1,648				—				3,803
Ending balance		$	43,995			$	29,056			$	3,955			$	77,006
Allowance for loan losses balance at September 30, 2014 attributable to:
Loans individually evaluated for impairment		$	1,175			$	328			$	—			$	1,503
Loans collectively evaluated for impairment		42,820				28,228				3,955				75,003
Loans acquired with deteriorated credit quality		—				500				—				500
Total		$	43,995			$	29,056			$	3,955			$	77,006
Recorded investment (loan balance) at September 30, 2014:
Loans individually evaluated for impairment		$	84,103			$	19,629			$	—			$	103,732
Loans collectively evaluated for impairment		2,388,586				2,285,296				—				4,673,882
Loans acquired with deteriorated credit quality		226,119				37,187				—				263,306
Total		$	2,698,808			$	2,342,112			$	—			$	5,040,920
The following schedule presents, by loan portfolio segment, details regarding the balance in the allowance and the recorded investment in loans at December 31, 2013 by impairment evaluation method.
		Commercial				Consumer				Unallocated				Total
		Loan				Loan
		Portfolio				Portfolio
		(In thousands)
Allowance for loan losses balance at December 31, 2013 attributable to:
Loans individually evaluated for impairment		$	1,081			$	510			$	—			$	1,591
Loans collectively evaluated for impairment		43,401				29,135				4,445				76,981
Loans acquired with deteriorated credit quality		—				500				—				500
Total		$	44,482			$	30,145			$	4,445			$	79,072
Recorded investment (loan balance) at December 31, 2013:
Loans individually evaluated for impairment		$	89,905			$	17,408			$	—			$	107,313
Loans collectively evaluated for impairment		2,178,714				2,066,897				—				4,245,611
Loans acquired with deteriorated credit quality		250,207				44,490				—				294,697
Total		$	2,518,826			$	2,128,795			$	—			$	4,647,621
The following schedule presents, by loan portfolio segment, the changes in the allowance for the three and nine months ended September 30, 2013 and details regarding the balance in the allowance and the recorded investment in loans at September 30, 2013 by impairment evaluation method.
		Commercial				Consumer				Unallocated				Total
		Loan				Loan
		Portfolio				Portfolio
		(In thousands)
Changes in allowance for loan losses for the three months ended September 30, 2013:
Beginning balance		$	47,780			$	28,745			$	5,659			$	82,184
Provision for loan losses		2,810				2,165				(1,975		)		3,000
Charge-offs		(2,637		)		(1,793		)		—				(4,430		)
Recoveries		374				404				—				778
Ending balance		$	48,327			$	29,521			$	3,684			$	81,532
Changes in allowance for loan losses for the nine months ended September 30, 2013:
Beginning balance		$	49,975			$	29,333			$	5,183			$	84,491
Provision for loan losses		5,815				4,684				(1,499		)		9,000
Charge-offs		(9,374		)		(5,891		)		—				(15,265		)
Recoveries		1,911				1,395				—				3,306
Ending balance		$	48,327			$	29,521			$	3,684			$	81,532
Allowance for loan losses balance at September 30, 2013 attributable to:
Loans individually evaluated for impairment		$	3,638			$	585			$	—			$	4,223
Loans collectively evaluated for impairment		44,689				28,436				3,684				76,809
Loans acquired with deteriorated credit quality		—				500				—				500
Total		$	48,327			$	29,521			$	3,684			$	81,532
Recorded investment (loan balance) at September 30, 2013:
Loans individually evaluated for impairment		$	78,782			$	17,731			$	—			$	96,513
Loans collectively evaluated for impairment		2,105,006				2,012,209				—				4,117,215
Loans acquired with deteriorated credit quality		261,999				46,944				—				308,943
Total		$	2,445,787			$	2,076,884			$	—			$	4,522,671
The allowance attributable to acquired loans of $0.5 million at September 30, 2014, December 31, 2013 and September 30, 2013 was primarily attributable to two consumer loan pools in the acquired loan portfolio that had a decline in expected cash flows. Management determined that the overall credit quality of the acquired loan portfolio had improved at September 30, 2014, which has resulted in an improvement in expected cash flows of loan pools in the acquired commercial loan portfolio. Accordingly, management reclassified $10.0 million during the nine months ended September 30, 2014 from the nonaccretable difference to the accretable yield for these acquired commercial loan pools, which will increase amounts recognized into interest income over the estimated remaining lives of these loan pools. There were no material changes in expected cash flows for the remaining acquired loan pools at September 30, 2014, December 31, 2013 or September 30, 2013.

Intangible_Assets

Intangible Assets	9 Months Ended
	Sep. 30, 2014
Goodwill and Intangible Assets Disclosure [Abstract]	'
Intangible Assets	'
	Intangible Assets
	The Corporation has the following types of intangible assets: goodwill, core deposit intangible assets and mortgage servicing rights (MSRs). Goodwill and core deposit intangible assets arose as the result of business combinations or other acquisitions. MSRs arose as a result of selling residential mortgage loans in the secondary market while retaining the right to service these loans and receive servicing income over the life of the loan. Amortization is recorded on the core deposit intangible assets and MSRs. Goodwill is not amortized but is evaluated at least annually for impairment. The Corporation’s most recent annual goodwill impairment test performed as of October 31, 2013 did not indicate that an impairment of goodwill existed. The Corporation also determined that no triggering events have occurred that indicated impairment from the most recent valuation date through September 30, 2014 and that the Corporation's goodwill was not impaired at September 30, 2014.
	The following table shows the net carrying value of the Corporation’s intangible assets:
		September 30,			December 31,			September 30,
		2014			2013			2013
		(In thousands)
	Goodwill	$	120,164		$	120,164		$	120,164
	Other intangible assets:
	Core deposit intangible assets	$	8,665		$	10,001		$	10,466
	Mortgage servicing rights	3,293			3,423			3,399
	Total other intangible assets	$	11,958		$	13,424		$	13,865
	The following table sets forth the carrying amount, accumulated amortization and amortization expense of core deposit intangible assets that are amortizable and arose from business combinations or other acquisitions:
		September 30,			December 31,			September 30,
		2014			2013			2013
		(In thousands)
	Gross original amount	$	18,659		$	18,659		$	18,659
	Accumulated amortization	9,994			8,658			8,193
	Carrying amount	$	8,665		$	10,001		$	10,466
	Amortization expense for the three months ended September 30	$	445					$	467
	Amortization expense for the nine months ended September 30	$	1,336					$	1,444
	The estimated future amortization expense on core deposit intangible assets for periods ending after September 30, 2014 is as follows: 2014 — $0.4 million; 2015 — $1.7 million; 2016 — $1.5 million; 2017 — $1.2 million; 2018 — $1.2 million; 2019 and thereafter — $2.7 million.
	The following shows the net carrying value and fair value of MSRs and the total loans that the Corporation is servicing for others:
		September 30,			December 31,			September 30,
		2014			2013			2013
		(In thousands)
	Net carrying value of MSRs	$	3,293		$	3,423		$	3,399
	Fair value of MSRs	$	6,618		$	6,878		$	6,839
	Loans serviced for others that have servicing rights capitalized	$	875,720		$	886,730		$	886,980
	The following table shows the activity for capitalized MSRs:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
		(In thousands)
	Balance at beginning of period	$	3,344		$	3,421		$	3,423		$	3,478
	Additions	324			311			745			1,271
	Amortization	(375		)	(333		)	(875		)	(1,350		)
	Balance at end of period	$	3,293		$	3,399		$	3,293		$	3,399
	There was no impairment valuation allowance recorded on MSRs as of September 30, 2014, December 31, 2013 or September 30, 2013.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Loss	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Accumulated Other Comprehensive Loss	'
	Accumulated Other Comprehensive Loss
	The components of accumulated other comprehensive loss, net of related tax benefit/expense, were as follows:
		September 30,			December 31,			September 30,
		2014			2013			2013
		(In thousands)
	Net unrealized losses on investment securities – available-for-sale, net of related tax benefit of $185 at September 30, 2014, $1,335 at December 31, 2013 and $878 at September 30, 2013	$	(344	)	$	(2,480	)	$	(1,631	)
	Pension and other postretirement benefits adjustment, net of related tax benefit of $10,318 at September 30, 2014, $9,714 at December 31, 2013 and $18,062 at September 30, 2013	(19,162		)	(18,040		)	(33,544		)
	Accumulated other comprehensive loss	$	(19,506	)	$	(20,520	)	$	(35,175	)

Regulatory_Capital

Regulatory Capital	9 Months Ended
	Sep. 30, 2014
Banking and Thrift [Abstract]	'
Regulatory Capital	'
	Regulatory Capital
	Federal and state banking regulations place certain restrictions on the transfer of assets, in the form of dividends, loans, or advances, from Chemical Bank to the Corporation. As of September 30, 2014, substantially all of the assets of Chemical Bank were restricted from transfer to the Corporation in the form of loans or advances. Dividends from Chemical Bank are the principal source of funds for the Corporation. At September 30, 2014, Chemical Bank was "well-capitalized" as defined by federal banking regulations. In addition to the statutory limits, the Corporation considers the overall financial and capital position of Chemical Bank prior to making any cash dividend decisions.
	The Corporation and Chemical Bank are subject to various regulatory capital requirements administered by federal banking agencies. Under these capital requirements, Chemical Bank must meet specific capital guidelines that involve quantitative measures of assets and certain off-balance sheet items as calculated under regulatory accounting practices. In addition, capital amounts and classifications are subject to qualitative judgments by regulators. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Corporation’s consolidated financial statements.
	Quantitative measures established by regulation to ensure capital adequacy require minimum ratios of Tier 1 capital to average assets (Leverage Ratio) and Tier 1 and Total capital to risk-weighted assets. These capital guidelines assign risk weights to on- and off-balance sheet items in arriving at total risk-weighted assets. Minimum capital levels are based upon the perceived risk of various asset categories and certain off-balance sheet instruments. Risk weighted assets of the Corporation totaled $5.06 billion, $4.64 billion and $4.51 billion at September 30, 2014, December 31, 2013 and September 30, 2013, respectively.
	At September 30, 2014, December 31, 2013 and September 30, 2013, Chemical Bank’s capital ratios exceeded the quantitative capital ratios required for an institution to be considered “well-capitalized.” Significant factors that may affect capital adequacy include, but are not limited to, a disproportionate growth in assets versus capital and a change in mix or credit quality of assets.
	The summary below compares the Corporation’s and Chemical Bank’s actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy:
		Actual				Minimum Required for Capital Adequacy Purposes				Required to be Well Capitalized Under Prompt Corrective Action Regulations
		Capital		Ratio		Capital		Ratio		Capital		Ratio
		Amount				Amount				Amount
		(Dollars in thousands)
	30-Sep-14
	Total Capital to Risk-Weighted Assets:
	Corporation	$	760,324	15	%	$	404,420	8	%	N/A		N/A
	Chemical Bank	613,673		12.2		403,840		8		$	504,799	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	696,963		13.8		202,210		4		N/A		N/A
	Chemical Bank	550,401		10.9		201,920		4		302,880		6
	Leverage Ratio:
	Corporation	696,963		11.1		251,133		4		N/A		N/A
	Chemical Bank	550,401		8.8		250,986		4		313,732		5
	31-Dec-13
	Total Capital to Risk-Weighted Assets:
	Corporation	$	649,836	14	%	$	371,465	8	%	N/A		N/A
	Chemical Bank	579,494		12.5		370,881		8		$	463,601	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	591,535		12.7		185,732		4		N/A		N/A
	Chemical Bank	521,283		11.2		185,440		4		278,160		6
	Leverage Ratio:
	Corporation	591,535		9.9		239,010		4		N/A		N/A
	Chemical Bank	521,283		8.7		238,884		4		298,605		5
	30-Sep-13
	Total Capital to Risk-Weighted Assets:
	Corporation	$	638,786	14.2	%	$	361,199	8	%	N/A		N/A
	Chemical Bank	568,626		12.6		360,617		8		$	450,771	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	582,039		12.9		180,600		4		N/A		N/A
	Chemical Bank	511,969		11.4		180,309		4		270,463		6
	Leverage Ratio:
	Corporation	582,039		10		232,972		4		N/A		N/A
	Chemical Bank	511,969		8.8		232,828		4		291,034		5

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements
	Fair value, as defined by GAAP, is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. A fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability or, in the absence of a principal market, the most advantageous market for the asset or liability. The price in the principal (or most advantageous) market used to measure the fair value of the asset or liability is not adjusted for transaction costs. An orderly transaction is a transaction that assumes exposure to the market for a period prior to the measurement date to allow for market activities that are usual and customary for transactions involving such assets and liabilities; it is not a forced transaction. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact and (iv) willing to transact.
	The Corporation utilizes fair value measurements to record fair value adjustments to certain assets and to determine fair value disclosures. Investment securities — available-for-sale and loans held-for-sale are recorded at fair value on a recurring basis. Additionally, the Corporation may be required to record other assets, such as impaired loans, goodwill, other intangible assets, other real estate and repossessed assets, at fair value on a nonrecurring basis. These nonrecurring fair value adjustments typically involve the application of lower of cost or market accounting or write-downs of individual assets.
	The Corporation determines the fair value of its financial instruments based on a three-level hierarchy established by GAAP. The classification and disclosure of assets and liabilities within the hierarchy is based on whether the inputs to the valuation methodology used for measurement are observable or unobservable. Observable inputs reflect market-derived or market-based information obtained from independent sources, while unobservable inputs reflect management’s estimates about market data. The three levels of inputs that may be used to measure fair value within the GAAP hierarchy are as follows:
	Level 1	Valuation is based upon quoted prices for identical instruments traded in active markets. Level 1 valuations for the Corporation would include U.S. Treasury securities that are traded by dealers or brokers in active over-the-counter markets. Valuations are obtained from a third-party pricing service for these investment securities.
	Level 2	Valuation is based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-based valuation techniques for which all significant assumptions are observable in the market. Level 2 valuations for the Corporation include government sponsored agency securities, including securities issued by the Federal Home Loan Bank, Federal Home Loan Mortgage Corporation, Federal National Mortgage Association, Federal Farm Credit Bank, Student Loan Marketing Corporation and the Small Business Administration, securities issued by certain state and political subdivisions, residential mortgage-backed securities, collateralized mortgage obligations, corporate bonds and preferred stock. Valuations are obtained from a third-party pricing service for these investment securities.
	Level 3	Valuation is generated from model-based techniques that use at least one significant assumption not observable in the market. These unobservable assumptions reflect estimates of assumptions that market participants would use in pricing the asset or liability. Valuation techniques include use of option pricing models, discounted cash flow models, yield curves and similar techniques. The determination of fair value requires management judgment or estimation and generally is corroborated by external data, which includes third-party pricing services. Level 3 valuations for the Corporation include securities issued by certain state and political subdivisions, trust preferred investment securities, impaired loans, goodwill, core deposit intangible assets, MSRs and other real estate and repossessed assets.
	A description of the valuation methodologies used for instruments measured at fair value, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below. These valuation methodologies were applied to all of the Corporation’s financial assets and financial liabilities carried at fair value and all financial instruments disclosed at fair value. In general, fair value is based upon quoted market prices, where available. If quoted market prices are not available, fair value is based upon third-party pricing services when available. Fair value may also be based on internally developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be required to record financial instruments at fair value. Any such valuation adjustments are applied consistently over time. The Corporation’s valuation methodologies may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values.
	While management believes the Corporation’s valuation methodologies are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. Furthermore, the fair value amounts may change significantly after the date of the statement of financial position from the amounts reported in the consolidated financial statements and related notes.
	Assets and Liabilities Recorded at Fair Value on a Recurring Basis
	Investment securities — available-for-sale are recorded at fair value on a recurring basis. Fair value measurement is based upon quoted prices, if available. If quoted prices are not available, fair values are generally measured using independent pricing models or other model-based valuation techniques that include market inputs, such as benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data and industry and economic events.
	The Corporation elected the fair value option for all residential mortgage loans held-for-sale originated on or after July 1, 2012. Accordingly, loans held-for-sale are recorded at fair value on a recurring basis. The fair values of loans held-for-sale are based on the market price for similar loans sold in the secondary market, and therefore, are classified as Level 2 valuations.
	Disclosure of Recurring Basis Fair Value Measurements
	For assets measured at fair value on a recurring basis, quantitative disclosures about the fair value measurements for each major category of assets were as follows:
			Fair Value Measurements – Recurring Basis
			Quoted Prices			Significant			Significant			Total
			In Active			Other			Unobservable
			Markets for			Observable			Inputs
			Identical			Inputs			(Level 3)
			Assets			(Level 2)
			(Level 1)
			(In thousands)
	30-Sep-14
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—		$	76,938		$	—		$	76,938
	State and political subdivisions		—			40,964			—			40,964
	Residential mortgage-backed securities		—			251,039			—			251,039
	Collateralized mortgage obligations		—			140,445			—			140,445
	Corporate bonds		—			65,183			—			65,183
	Preferred stock		—			1,642			—			1,642
	Total investment securities – available-for-sale		—			576,211			—			576,211
	Loans held-for-sale		—			9,347			—			9,347
	Total assets measured at fair value on a recurring basis		$	—		$	585,558		$	—		$	585,558
	31-Dec-13
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—		$	93,763		$	—		$	93,763
	State and political subdivisions		—			43,798			—			43,798
	Residential mortgage-backed securities		—			299,366			—			299,366
	Collateralized mortgage obligations		—			180,941			—			180,941
	Corporate bonds		—			65,275			—			65,275
	Preferred stock		—			1,427			—			1,427
	Total investment securities – available-for-sale		—			684,570			—			684,570
	Loans held-for-sale		—			5,219			—			5,219
	Total assets measured at fair value on a recurring basis		$	—		$	689,789		$	—		$	689,789
	30-Sep-13
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—		$	85,925		$	—		$	85,925
	State and political subdivisions		—			45,572			—			45,572
	Residential mortgage-backed securities		—			308,160			—			308,160
	Collateralized mortgage obligations		—			198,458			—			198,458
	Corporate bonds		—			65,434			—			65,434
	Preferred stock		—			1,597			—			1,597
	Total investment securities – available-for-sale		—			705,146			—			705,146
	Loans held-for-sale		—			7,907			—			7,907
	Total assets measured at fair value on a recurring basis		$	—		$	713,053		$	—		$	713,053
	There were no liabilities recorded at fair value on a recurring basis at September 30, 2014, December 31, 2013 or September 30, 2013.
	Assets and Liabilities Recorded at Fair Value on a Nonrecurring Basis
	The Corporation does not record loans held for investment at fair value on a recurring basis. However, from time to time, a loan is considered impaired and an allocation of the allowance (valuation allowance) may be established or a portion of the loan is charged off. Loans for which it is probable that payment of interest and principal will not be made in accordance with the contractual terms of the loan agreement are considered impaired. The fair value of impaired loans is estimated using one of several methods, including the loan’s observable market price, the fair value of the collateral or the present value of the expected future cash flows discounted at the loan’s effective interest rate. Those impaired loans not requiring a valuation allowance represent loans for which the fair value of the expected repayments or collateral exceed the remaining carrying amount of such loans. Impaired loans where a valuation allowance is established or a portion of the loan is charged off based on the fair value of collateral are subject to nonrecurring fair value measurement and require classification in the fair value hierarchy. The Corporation records impaired loans as Level 3 valuations as there is generally no observable market price or independent appraised value, or management determines the fair value of the collateral is further impaired below the appraised value. When management determines the fair value of the collateral is further impaired below appraised value, discount factors ranging between 70% and 80% of the appraised value are used depending on the nature of the collateral and the age of the most recent appraisal.
	Goodwill is subject to impairment testing on an annual basis. The assessment of goodwill for impairment requires a significant degree of judgment. In the event the assessment indicates that it is more-likely-than-not that the fair value is less than the carrying value, the asset is considered impaired and recorded at fair value. Goodwill that is impaired and subject to nonrecurring fair value measurements is a Level 3 valuation. At September 30, 2014, December 31, 2013 and September 30, 2013, no goodwill was impaired, and therefore, goodwill was not recorded at fair value on a nonrecurring basis.
	Other intangible assets consist of core deposit intangible assets and MSRs. These items are both recorded at fair value when initially recorded. Subsequently, core deposit intangible assets are amortized primarily on an accelerated basis over periods ranging from ten to fifteen years and are subject to impairment testing whenever events or changes in circumstances indicate that the carrying amount exceeds the fair value of the asset. If core deposit intangible asset impairment is identified, the Corporation classifies impaired core deposit intangible assets subject to nonrecurring fair value measurements as Level 3 valuations. The fair value of MSRs is initially estimated using a model that calculates the net present value of estimated future cash flows using various assumptions, including prepayment speeds, the discount rate and servicing costs. If the valuation model reflects a value less than the carrying value, MSRs are adjusted to fair value, as determined by the model, through a valuation allowance. The Corporation classifies MSRs subject to nonrecurring fair value measurements as Level 3 valuations. At September 30, 2014, December 31, 2013 and September 30, 2013, there was no impairment identified for core deposit intangible assets or MSRs and, therefore, no other intangible assets were recorded at fair value on a nonrecurring basis.
	The carrying amounts for other real estate (ORE) and repossessed assets (RA) are reported in the consolidated statements of financial position under “Interest receivable and other assets.” ORE and RA include real estate and other types of assets repossessed by the Corporation. ORE and RA are recorded at the lower of cost or fair value upon the transfer of a loan to ORE or RA and, subsequently, ORE and RA continue to be measured and carried at the lower of cost or fair value. Fair value is based upon independent market prices, appraised values of the property or management’s estimation of the value of the property. The Corporation records ORE and RA as Level 3 valuations as management generally determines that the fair value of the property is impaired below the appraised value. When management determines the fair value of the property is further impaired below appraised value, discount factors ranging between 70% and 75% of the appraised value are used depending on the nature of the property and the age of the most recent appraisal.
	Disclosure of Nonrecurring Basis Fair Value Measurements
	For assets measured at fair value on a nonrecurring basis, quantitative disclosures about fair value measurements for each major category of assets were as follows:
		Fair Value Measurements – Nonrecurring Basis
		Quoted Prices			Significant			Significant			Total
		In Active			Other			Unobservable
		Markets for			Observable			Inputs
		Identical			Inputs			(Level 3)
		Assets			(Level 2)
		(Level 1)
		(In thousands)
30-Sep-14
Impaired originated loans		$	—		$	—		$	26,037		$	26,037
Other real estate/repossessed assets		—			—			10,354			10,354
Total		$	—		$	—		$	36,391		$	36,391
31-Dec-13
Impaired originated loans		$	—		$	—		$	28,852		$	28,852
Other real estate/repossessed assets		—			—			9,776			9,776
Total		$	—		$	—		$	38,628		$	38,628
30-Sep-13
Impaired originated loans		$	—		$	—		$	39,535		$	39,535
Other real estate/repossessed assets		—			—			12,033			12,033
Total		$	—		$	—		$	51,568		$	51,568
There were no liabilities recorded at fair value on a nonrecurring basis at September 30, 2014, December 31, 2013 and September 30, 2013.
Disclosures about Fair Value of Financial Instruments
GAAP requires disclosures about the estimated fair value of the Corporation's financial instruments, including those financial assets and liabilities that are not measured and reported at fair value on a recurring or nonrecurring basis. However, the method of estimating fair value for certain financial instruments, such as loans, that are not required to be measured on a recurring or nonrecurring basis, as prescribed by ASC 820, Fair Value Measurements and Disclosures, does not incorporate the exit-price concept of fair value. The Corporation utilized the fair value hierarchy in computing the fair values of its financial instruments. In cases where quoted market prices were not available, the Corporation employed present value methods using unobservable inputs requiring management's judgment to estimate the fair values of its financial instruments, which are considered Level 3 valuations. These Level 3 valuations are affected by the assumptions made and, accordingly, do not necessarily indicate amounts that could be realized in a current market exchange. It is also the Corporation's general practice and intent to hold the majority of its financial instruments until maturity and, therefore, the Corporation does not expect to realize the estimated amounts disclosed.
The methodologies for estimating the fair value of financial assets and financial liabilities on a recurring or nonrecurring basis are discussed above. At September 30, 2014, December 31, 2013 and September 30, 2013, the estimated fair values of cash and cash equivalents, interest receivable and interest payable approximated their carrying values at those dates. The methodologies for other financial assets and financial liabilities follow.
Fair value measurement for investment securities — held-to-maturity is based upon quoted prices, if available. If quoted prices are not available, fair values are measured using independent pricing models or other model-based valuation techniques that include market inputs such as benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data and industry and economic events. Fair value measurements using Level 2 valuations of investment securities — held-to-maturity include the majority of the Corporation's investment securities issued by state and political subdivisions. Level 3 valuations include certain securities issued by state and political subdivisions and trust preferred investment securities.
Fair value measurements of nonmarketable equity securities, which consisted of Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock, are based on their redeemable value, which is cost. The market for these securities is restricted to the issuer of the stock and subject to impairment evaluation. It is not practicable to determine the fair value of these securities within the fair value hierarchy due to the restrictions placed on their transferability.
Loans held-for-sale are carried at fair value, as the Corporation elected the fair value option on these loans. The fair values of loans held-for-sale are based on the market price for similar loans sold in the secondary market, and therefore, are classified as Level 2 valuations.
The fair value of variable interest rate loans that reprice regularly with changes in market interest rates are based on carrying values. The fair values for fixed interest rate loans are estimated using discounted cash flow analyses, using the Corporation’s interest rates currently being offered for loans with similar terms to borrowers of similar credit quality. The resulting fair value amounts are adjusted to estimate the impact of changes in the credit quality of borrowers after the loans were originated. The fair value measurements for loans are Level 3 valuations.
The fair values of deposit accounts without defined maturities, such as interest- and noninterest-bearing checking, savings and money market accounts, are equal to the amounts payable on demand. Fair value measurements for fixed-interest rate time deposits with defined maturities are based on the discounted value of contractual cash flows, using the Corporation’s interest rates currently being offered for deposits of similar maturities, and are Level 3 valuations. The fair values for variable-interest rate time deposits with defined maturities approximate their carrying amounts.
Short-term borrowings consist of securities sold under agreements to repurchase and federal funds purchased. Fair value measurements for short-term borrowings are based on the present value of future estimated cash flows using current interest rates offered to the Corporation for debt with similar terms and are Level 2 valuations.
Fair value measurements for FHLB advances are estimated based on the present value of future estimated cash flows using current interest rates offered to the Corporation for debt with similar terms and are Level 2 valuations.
The Corporation’s unused commitments to extend credit, standby letters of credit and loan commitments have no carrying amount and have been estimated to have no realizable fair value. Historically, a majority of the unused commitments to extend credit have not been drawn upon and, generally, the Corporation does not receive fees in connection with these commitments other than standby letter of credit fees, which are not significant.
Fair value measurements have not been made for items that are not defined by GAAP as financial instruments, including such items as the value of the Corporation’s Wealth Management department and the value of the Corporation’s core deposit base. The Corporation believes it is impractical to estimate a representative fair value for these types of assets, even though management believes they add significant value to the Corporation.
A summary of carrying amounts and estimated fair values of the Corporation’s financial instruments included in the consolidated statements of financial position was as follows:
	Level in Fair Value Measurement		30-Sep-14						31-Dec-13					30-Sep-13
	Hierarchy		Carrying			Fair			Carrying			Fair		Carrying		Fair
			Amount			Value			Amount			Value		Amount		Value
			(In thousands)
Assets:
Cash and cash equivalents	Level 1		$	382,138		$	382,138		$	310,788		$	310,788	$	493,110	$	493,110
Investment securities:
Available-for-sale	Level 2		576,211			576,211			684,570			684,570		705,146		705,146
Held-to-maturity	Level 2		308,062			307,290			263,405			262,021		272,079		269,616
Held-to-maturity	Level 3		10,500			6,985			10,500			6,250		10,500		6,250
Nonmarketable equity securities	NA		25,572			25,572			25,572			25,572		25,572		25,572
Loans held-for-sale	Level 2		9,347			9,347			5,219			5,219		7,907		7,907
Net loans	Level 3		4,963,914			4,967,167			4,568,549			4,575,532		4,441,139		4,446,796
Interest receivable	Level 2		17,057			17,057			15,748			15,748		16,359		16,359
Liabilities:
Deposits without defined maturities	Level 2		$	4,191,894		$	4,191,894		$	3,790,454		$	3,790,454	$	3,842,148	$	3,842,148
Time deposits	Level 3		1,240,033			1,242,419			1,331,931			1,340,746		1,349,157		1,359,739
Interest payable	Level 2		710			710			868			868		1,009		1,009
Short-term borrowings	Level 2		323,086			323,086			327,428			327,428		357,595		357,595

Earnings_Per_Common_Share

Earnings Per Common Share	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Earnings Per Common Share	'
	Earnings Per Common Share
	Basic earnings per common share for the Corporation is computed by dividing net income by the weighted average number of common shares outstanding during the period. Basic earnings per common share excludes any dilutive effect of common stock equivalents.
	Diluted earnings per common share for the Corporation is computed by dividing net income by the sum of the weighted average number of common shares outstanding and the dilutive effect of common stock equivalents using the treasury stock method. Average shares of common stock for diluted net income per common share include shares to be issued upon the exercise of stock options granted under the Corporation’s share-based compensation plans, restricted stock units that may be converted to stock, stock to be issued under the deferred stock compensation plan for non-employee directors and stock to be issued under the stock purchase plan for non-employee advisory directors. For any period in which a net loss is recorded, the assumed exercise of stock options, restricted stock units that may be converted to stock and stock to be issued under the deferred stock compensation plan and the stock purchase plan would have an anti-dilutive impact on the net loss per common share and thus are excluded in the diluted earnings per common share calculation.
	The following summarizes the numerator and denominator of the basic and diluted earnings per common share computations:
		Three Months Ended September 30,				Nine Months Ended September 30,
		2014		2013		2014		2013
		(In thousands, except per share data)
	Numerator for both basic and diluted earnings per common share, net income	$	16,767	$	14,993	$	46,816	$	42,430
	Denominator for basic earnings per common share, weighted average common shares outstanding	32,762		27,870		30,896		27,642
	Weighted average common stock equivalents	194		167		205		144
	Denominator for diluted earnings per common share	32,956		28,037		31,101		27,786
	Basic earnings per common share	$	0.51	$	0.54	$	1.52	$	1.54
	Diluted earnings per common share	0.51		0.53		1.51		1.53
	The average number of exercisable employee stock option awards outstanding that were “out-of-the-money,” whereby the option exercise price per share exceeded the market price per share and, therefore, were not included in the computation of diluted earnings per common share because they would have been anti-dilutive totaled 249,150 and 308,009 for the three months ended September 30, 2014 and 2013, respectively, and 251,403 and 377,847 for the nine months ended September 30, 2014 and 2013, respectively.

ShareBased_Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Share-Based Compensation	'
	Share-Based Compensation
	The Corporation maintains a share-based compensation plan under which it periodically grants share-based awards for a fixed number of shares to certain officers of the Corporation. The fair value of share-based awards is recognized as compensation expense over the requisite service or performance period. During the three-month periods ended September 30, 2014 and 2013, share-based compensation expense related to stock options and restricted stock units totaled $0.7 million and $0.8 million, respectively. During the nine-month periods ended September 30, 2014 and 2013, share-based compensation expense related to stock options and restricted stock units totaled $1.9 million and $2.1 million, respectively.
	During the nine-month period ended September 30, 2014, the Corporation granted options to purchase 190,011 shares of common stock and 68,619 restricted stock units to certain officers. At September 30, 2014, there were 429,111 shares of common stock available for future grants under the share-based compensation plan.
	Stock Options
	The Corporation issues stock options to certain officers. Stock options are issued at the current market price of the Corporation's common stock on the date of grant and expire ten years from the date of grant. Beginning in 2013, stock options granted vest ratably over a five-year period. Stock options granted prior to 2013 generally vest ratably over a three-year period.
	A summary of activity for the Corporation’s stock options as of and for the nine months ended September 30, 2014 is presented below:
			Non-Vested						Stock Options Outstanding
			Stock Options Outstanding
			Number of		Weighted-		Weighted-		Number of		Weighted-
			Options		Average		Average		Options		Average
					Exercise		Grant Date				Exercise
					Price		Fair Value Per Share				Price
					Per Share						Per Share
	Outstanding at January 1, 2014		414,080		$	24.29	$	7.19	1,073,990		$	26.84
	Granted		190,011		29.45		9.64		190,011		29.45
	Exercised		—		—		—		(66,130	)	24.91
	Vested		(148,016	)	23.43		6.98		—		—
	Forfeited/expired		(14,869	)	25.69		7.8		(16,256	)	26.62
	Outstanding at September 30, 2014		441,206		$	26.75	$	8.3	1,181,615		$	27.37
	Exercisable/vested at September 30, 2014								740,409		$	27.75
	The weighted-average remaining contractual terms were 5.7 years for all outstanding stock options and 3.8 years for exercisable stock options at September 30, 2014. The intrinsic value of all outstanding in-the-money stock options and exercisable in-the-money stock options was $2.2 million and $1.7 million, respectively, at September 30, 2014. The aggregate intrinsic values of outstanding and exercisable options at September 30, 2014 were calculated based on the closing market price of the Corporation’s common stock on September 30, 2014 of $26.89 per share less the exercise price. Options with intrinsic values less than zero, or “out-of-the-money” options, were not included in the aggregate intrinsic value reported.
	At September 30, 2014, unrecognized compensation expense related to stock options totaled $3.0 million and is expected to be recognized over a remaining weighted average period of 3.7 years.
	The fair value of the stock options granted during the nine months ended September 30, 2014 was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions.
	Expected dividend yield	3		%
	Risk-free interest rate	2.16		%
	Expected stock price volatility	42.2		%
	Expected life of options – in years	7
	Weighted average fair value of options granted	$	9.64
	Restricted Stock Units
	In addition to stock options, the Corporation grants restricted stock performance units and restricted stock service-based units (collectively referred to as restricted stock units) to certain officers. The restricted stock performance units vest based on the Corporation achieving certain performance target levels. The restricted stock performance units are eligible to vest from 0.25x to 1.5x the number of units originally granted depending on which, if any, of the performance target levels are met. However, if the minimum performance target level is not achieved, no shares will become vested or be issued for that respective year’s restricted stock performance units. The restricted stock service-based units vest upon satisfaction of a service condition. Upon achievement of the performance target level and/or satisfaction of a service condition, if applicable, the restricted stock units are converted into shares of the Corporation’s common stock on a one-to-one basis. Compensation expense related to restricted stock units is recognized over the expected requisite performance or service period, as applicable.
	A summary of the activity for restricted stock units as of and for the nine months ended September 30, 2014 is presented below:
			Number of		Weighted-
			Units		Average
					Grant Date
					Fair Value
					Per Unit
	Outstanding at January 1, 2014		188,532		$	21.49
	Granted		68,619		27.49
	Converted into shares of common stock		(51,895	)	19.21
	Forfeited/expired		(4,813	)	23.84
	Outstanding at September 30, 2014		200,443		$	24.08
	At September 30, 2014, unrecognized compensation expense related to restricted stock unit awards totaled $2.7 million and is expected to be recognized over a remaining weighted average period of 2.6 years.

Pension_and_Other_Postretireme

Pension and Other Postretirement Benefit Plans	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Pension and Other Postretirement Benefit Plans	'
	Pension and Other Postretirement Benefit Plans
	The components of net periodic benefit cost for the Corporation’s qualified and nonqualified pension plans and nonqualified postretirement benefit plan are as follows:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
		(In thousands)
	Defined Benefit Pension Plans
	Service cost	$	250		$	326		$	751		$	976
	Interest cost	1,312			1,166			3,936			3,500
	Expected return on plan assets	(2,078		)	(1,949		)	(6,235		)	(5,845		)
	Amortization of prior service credit	—			—			(1		)	(1		)
	Amortization of unrecognized net loss	569			946			1,707			2,838
	Net periodic benefit cost	$	53		$	489		$	158		$	1,468
	Postretirement Benefit Plan
	Service cost	$	5		$	5		$	14		$	14
	Interest cost	36			36			107			108
	Amortization of prior service cost	32			27			97			233
	Amortization of unrecognized net gain	(26		)	(18		)	(78		)	(55		)
	Net periodic benefit cost	$	47		$	50		$	140		$	300
	The Corporation’s pension plan does not have a contribution requirement in 2014. The Corporation made a $15.0 million contribution to the pension plan during the nine months ended September 30, 2013. The discount rate used to compute the Corporation's pension plan expense for 2014 is 5.00%.
	401(k) Savings Plan expense for the Corporation’s match of participants’ base compensation contributions and a 4% of eligible pay contribution to certain employees who are not grandfathered under the pension plan was $1.0 million and $0.9 million for the three months ended September 30, 2014 and 2013, respectively, and $2.7 million for both the nine months ended September 30, 2014 and 2013.

Financial_Guarantees

Financial Guarantees	9 Months Ended
	Sep. 30, 2014
Guarantees [Abstract]	'
Financial Guarantees	'
	Financial Guarantees
	In the normal course of business, the Corporation is a party to financial instruments containing credit risk that are not required to be reflected in the consolidated statements of financial position. For the Corporation, these financial instruments are financial and performance standby letters of credit. The Corporation has risk management policies to identify, monitor and limit exposure to credit risk. To mitigate credit risk for these financial guarantees, the Corporation generally determines the need for specific covenant, guarantee and collateral requirements on a case-by-case basis, depending on the nature of the financial instrument and the customer’s creditworthiness. At September 30, 2014, December 31, 2013 and September 30, 2013, the Corporation had $37 million, $47 million and $48 million, respectively, of outstanding financial and performance standby letters of credit that expire in five years or less. The majority of these standby letters of credit are collateralized. The Corporation determined that there were no potential losses from standby letters of credit at September 30, 2014, December 31, 2013 and September 30, 2013.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Nature of Operations	'
	Nature of Operations
	Chemical Financial Corporation (Corporation) operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operates through one commercial bank, Chemical Bank. Chemical Bank operates within the State of Michigan as a state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of four regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the bank’s geographical market areas. The products and services offered by the regional banking units, through branch banking offices, are generally consistent throughout the Corporation, as is the pricing of those products and services. The marketing of products and services throughout the Corporation’s regional banking units is generally uniform, as many of the markets served by the regional banking units overlap. The distribution of products and services is uniform throughout the Corporation’s regional banking units and is achieved primarily through retail branch banking offices, automated teller machines and electronically accessed banking products.
	The Corporation’s primary sources of revenue are interest from its loan products and investment securities, service charges and fees from customer deposit accounts and wealth management revenue.
Basis of Presentation	'
	Basis of Presentation
	The accompanying unaudited consolidated financial statements of the Corporation and its subsidiaries have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, the interim consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s consolidated financial statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2013. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments believed necessary to present fairly the financial condition and results of operations of the Corporation for the periods presented. Operating results for the nine months ended September 30, 2014 are not necessarily indicative of the results that may be expected for the year ending December 31, 2014.
Use of Estimates	'
	Use of Estimates
	Management makes estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying footnotes. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, expected cash flows from acquired loans, fair value amounts related to business combinations, pension expense, income taxes, goodwill impairment and those assets that require fair value measurement. Actual results could differ from these estimates.
Originated Loans	'
	Originated Loans
	Originated loans include all of the Corporation's portfolio loans, excluding loans acquired on April 30, 2010 in the acquisition of O.A.K. Financial Corporation (OAK). Originated loans also include loans acquired as part of the Corporation's branch acquisition on December 7, 2012, as these loans were performing and were considered high-quality loans in accordance with the Corporation's credit underwriting standards at that date. Originated loans are stated at their principal amount outstanding, net of unearned income, charge-offs and unamortized deferred fees and costs. Loan interest income is recognized on the accrual basis. Deferred loan fees and costs are amortized over the loan term based on the level-yield method. Net loan commitment fees are deferred and amortized into fee income on a straight-line basis over the commitment period.
	The past due status of a loan is based on the loan’s contractual terms. A loan is placed in nonaccrual status (accrual of interest is discontinued) when principal or interest is past due 90 days or more (except for a loan that is secured by residential real estate, which is transferred to nonaccrual status at 120 days past due), unless the loan is both well-secured and in the process of collection, or earlier when, in the opinion of management, there is sufficient reason to doubt the collectibility of principal or interest. Interest previously accrued, but not collected, is reversed and charged against interest income at the time the loan is placed in nonaccrual status. Subsequent receipts of interest while a loan is in nonaccrual status are recorded as a reduction of principal. Loans are returned to accrual status when principal and interest payments are brought current, payments have been received consistently for a period of time (generally six months) and collectibility is no longer in doubt.
Loans Acquired in a Business Combination	'
	Loans Acquired in a Business Combination
	Loans acquired in a business combination (acquired loans) consist of loans acquired on April 30, 2010 in the acquisition of OAK. Acquired loans were recorded at fair value at the date of acquisition, without a carryover of the associated allowance for loan losses related to these loans, through a fair value discount that was, in part, attributable to deterioration in credit quality. The estimate of expected credit losses was determined based on due diligence performed by executive and senior officers of the Corporation, with assistance from third-party consultants. The fair value discount was recorded as a reduction of the acquired loans’ outstanding principal balances in the consolidated statement of financial position at the acquisition date.
	The Corporation accounts for acquired loans, which are recorded at fair value at acquisition, in accordance with Accounting Standards Codification (ASC) Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality (ASC 310-30). ASC 310-30 allows investors to aggregate loans acquired into loan pools that have common risk characteristics and thereby use a composite interest rate and expectation of cash flows expected to be collected for the loan pools. Under the provisions of ASC 310-30, the Corporation aggregated acquired loans into 14 pools based upon common risk characteristics, including types of loans, commercial type loans with similar risk grades and whether loans were performing or nonperforming. A pool is considered a single unit of accounting for purposes of applying the guidance prescribed in ASC 310-30. A loan will be removed from a pool of acquired loans only if the loan is sold, foreclosed, paid off or written off, and will be removed from the pool at the carrying value. If an individual loan is removed from a pool of loans, the difference between its relative carrying amount and the cash, fair value of the collateral, or other assets received would not affect the effective yield used to recognize the accretable difference on the remaining pool. The Corporation estimated the cash flows expected to be collected over the life of the pools of loans at acquisition, and estimates expected cash flows quarterly thereafter, based on a set of assumptions including expectations as to default rates, prepayment rates and loss severities. The Corporation must make numerous assumptions, interpretations and judgments using internal and third-party credit quality information to determine whether it is probable that the Corporation will be able to collect all contractually required payments. This is a point in time assessment and inherently subjective due to the nature of the available information and judgment involved.
	The calculation of the fair value of the acquired loan pools entails estimating the amount and timing of cash flows attributable to both principal and interest expected to be collected on such loan pools and then discounting those cash flows at market interest rates. The excess of a loan pool's expected cash flows at the acquisition date over its estimated fair value is referred to as the "accretable yield," which is recognized into interest income over the estimated remaining life of the loan pool on a level-yield basis. The difference between a loan pool's contractually required principal and interest payments at the acquisition date and the cash flows expected to be collected at the acquisition date is referred to as the "nonaccretable difference," which includes an estimate of future credit losses expected to be incurred over the estimated life of the loan pool and interest payments that are not expected to be collected. Decreases to the expected cash flows in each loan pool in subsequent periods will require the Corporation to record a provision for loan losses. Improvements in expected cash flows in each loan pool in subsequent periods will result in reversing a portion of the nonaccretable difference, which is then classified as part of the accretable yield and subsequently recognized into interest income over the estimated remaining life of the loan pool.
Loans Modified Under Troubled Debt Restructurings	'
	Loans Modified Under Troubled Debt Restructurings
	Loans modified under troubled debt restructurings (TDRs) involve granting a concession to a borrower who is experiencing financial difficulty. Concessions generally include modifications to original loan terms, including changes to a loan’s payment schedule or interest rate, which generally would not otherwise be considered. The Corporation’s TDRs include performing and nonperforming TDRs, which consist of originated loans that continue to accrue interest at the loan's original interest rate as the Corporation expects to collect the remaining principal and interest on the loan, and nonaccrual TDRs, which include originated loans that are in a nonaccrual status and are no longer accruing interest, as the Corporation does not expect to collect the full amount of principal and interest owed from the borrower on these loans. At the time of modification (except for loans on nonaccrual status), a TDR is reported as a nonperforming TDR until a six-month payment history of principal and interest payments, in accordance with the terms of the loan modification, is sustained, at which time the Corporation moves the loan to a performing status (performing TDR). If the Corporation does not expect to collect all principal and interest on the loan, the modified loan is classified as a nonaccrual TDR. All TDRs are accounted for as impaired loans and are included in the Corporation’s analysis of the allowance for loan losses. A TDR that has been refinanced by a borrower who is no longer experiencing financial difficulty and which yields a market rate of interest at the time of a refinancing is no longer reported as a TDR.
	Loans in the Corporation’s commercial loan portfolio (comprised of commercial, commercial real estate, real estate construction and land development loans) that meet the definition of a TDR generally consist of loans where the Corporation has allowed borrowers to defer scheduled principal payments and make interest-only payments for a specified period of time at the stated interest rate of the original loan agreement or reduced payments due to a moderate extension of the loan’s contractual term. If the Corporation does not expect to collect all principal and interest on the loan, the modified loan is classified as a nonaccrual TDR. If the Corporation does not expect to incur a loss on the loan based on its assessment of the borrowers’ expected cash flows, as the pre- and post-modification effective yields are approximately the same, the loan is classified as a nonperforming TDR until a six-month payment history is sustained, at which time the loan is classified as a performing TDR. Since no loss is expected to be incurred on these loans, no additional provision for loan losses has been recognized related to these loans, and these loans accrue interest at their contractual interest rate. These loans are individually evaluated for impairment and transferred to nonaccrual status if they become 90 days past due as to principal or interest payments or if it is probable that any remaining principal and interest payments due on the loan will not be collected in accordance with the modified terms of the loans.
	Loans in the Corporation’s consumer loan portfolio (comprised of residential mortgage, consumer installment and home equity loans) that meet the definition of a performing or nonperforming TDR generally consist of residential mortgage loans that include a concession that reduces a borrower’s monthly payments by decreasing the interest rate charged on the loan for a specified period of time (generally 24 months) under a formal modification agreement. The Corporation recognizes an additional provision for loan losses related to impairment on these loans on an individual basis based on the present value of expected future cash flows discounted at the loan’s original effective interest rate. These loans continue to accrue interest at the loan's effective interest rate, which consists of contractual interest under the terms of the modification agreement in addition to an adjustment for the accretion of computed impairment. These loans are moved to nonaccrual status if they become 90 days past due as to principal or interest payments, or sooner if conditions warrant.
Impaired Loans	'
	Impaired Loans
	A loan is defined to be impaired when it is probable that payment of principal and interest will not be paid in accordance with the original contractual terms of the loan agreement. Impaired loans include nonaccrual loans (including nonaccrual TDRs), performing and nonperforming TDRs and acquired loans that were not performing in accordance with original contractual terms. Impaired loans are accounted for at the lower of the present value of expected cash flows discounted at the loan's original effective interest rate or the estimated fair value of the collateral, if the loan is collateral dependent. When the present value of expected cash flows or the fair value of collateral of an impaired loan in the originated loan portfolio is less than the amount of unpaid principal outstanding on the loan, the principal balance of the loan is reduced to its carrying value through either an allocation of the allowance for loan losses or a partial charge-off of the loan balance.
Nonperforming Loans	'
	Nonperforming Loans
	Nonperforming loans are comprised of loans for which the accrual of interest has been discontinued (nonaccrual loans, including nonaccrual TDRs), accruing originated loans contractually past due 90 days or more as to interest or principal payments and nonperforming TDRs.
	Acquired loans that were classified as nonperforming loans prior to being acquired and acquired loans that are not performing in accordance with contractual terms subsequent to acquisition are not classified as nonperforming loans subsequent to acquisition because the loans are recorded in pools at net realizable value based on the principal and interest the Corporation expects to collect on such loans.
Allowance for Loan Losses	'
	Allowance for Loan Losses
	The allowance for loan losses (allowance) is presented as a reserve against loans. The allowance represents management’s assessment of probable loan losses inherent in the Corporation’s loan portfolio.
	Management’s evaluation of the adequacy of the allowance is based on a continuing review of the loan portfolio, actual loan loss experience, the underlying value of the collateral, risk characteristics of the loan portfolio, the level and composition of nonperforming loans, the financial condition of the borrowers, the balance of the loan portfolio, loan growth, economic conditions, employment levels in the Corporation’s local markets, and special factors affecting specific business sectors. The Corporation maintains formal policies and procedures to monitor and control credit risk. Management evaluates the allowance on a quarterly basis in an effort to ensure the level is appropriate to absorb probable losses inherent in the loan portfolio.
	The allowance provides for probable losses that have been identified with specific customer relationships and for probable losses believed to be incurred in the remainder of the originated loan portfolio, but that have not been specifically identified. The Corporation utilizes its own loss experience to estimate inherent losses on loans. Internal risk ratings are assigned to each loan in the commercial loan portfolio (commercial, commercial real estate, real estate construction and land development loans) at the time of origination and are subject to subsequent periodic reviews by senior management. The Corporation performs a detailed credit quality review quarterly on all loans greater than $0.25 million that have deteriorated below certain levels of credit risk, and may allocate a specific portion of the allowance to such loans based upon this review. A portion of the allowance is allocated to the remaining loans by applying projected loss ratios, based on numerous factors. Projected loss ratios incorporate factors such as charge-off experience, trends with respect to adversely risk-rated loans in the commercial loan portfolio, trends with respect to past due and nonaccrual loans, changes in economic conditions and trends, changes in the value of underlying collateral and other credit risk factors. This evaluation involves a high degree of uncertainty.
	In determining the allowance and the related provision for loan losses, the Corporation considers four principal elements: (i) valuation allowances based upon probable losses identified during the review of impaired loans in the commercial loan portfolio, (ii) reserves established for adversely-rated loans in the commercial loan portfolio and nonaccrual residential mortgage, consumer installment and home equity loans based on loan loss experience of other adversely-rated loans, (iii) reserves, by loan classes, on all other loans based principally on a five-year historical loan loss experience, with higher weighting placed on the most recent years, and loan loss trends and (iv) an unallocated allowance based on the imprecision in the overall allowance methodology for loans collectively evaluated for impairment.
	Although the Corporation allocates portions of the allowance to specific loans and loan types, the entire allowance attributable to originated loans is available for any loan losses that occur in the originated portfolio. Loans that are deemed not collectible are charged off and reduce the allowance. The provision for loan losses and recoveries on loans previously charged off increase the allowance. Collection efforts may continue and recoveries may occur after a loan is charged off.
	Acquired loans are aggregated into pools based upon common risk characteristics. An allowance may be recorded related to an acquired loan pool if it experiences a decrease in expected cash flows, as compared to those projected at the acquisition date. On a quarterly basis, the expected future cash flow of each pool is estimated based on various factors, including changes in property values of collateral dependent loans, default rates, loss severities and prepayment speeds. Decreases in estimates of expected cash flows within a pool generally result in a charge to the provision for loan losses and a corresponding increase in the allowance allocated to acquired loans for the particular pool. Increases in estimates of expected cash flows within a pool generally result in a reduction in the allowance allocated to acquired loans for the particular pool, if applicable, and then an adjustment to the accretable yield for the pool, which will increase amounts recognized in interest income in subsequent periods.
	Various regulatory agencies, as an integral part of their examination process, periodically review the allowance. Such agencies may require additions to the allowance, based on their judgment, reflecting information available to them at the time of their examinations.
Fair Value Measurements	'
	Fair Value Measurements
	Fair value for assets and liabilities measured at fair value on a recurring or nonrecurring basis refers to the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants in the market in which the reporting entity transacts such sales or transfers based on the assumptions market participants would use when pricing an asset or liability. Assumptions are developed based on prioritizing information within a fair value hierarchy that gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data, such as the reporting entity’s own data.
	The Corporation may choose to measure eligible items at fair value at specified election dates. Unrealized gains and losses on items for which the fair value measurement option has been elected are reported in earnings at each subsequent reporting date. The fair value option (i) may be applied instrument by instrument, with certain exceptions, allowing the Corporation to record identical financial assets and liabilities at fair value or by another measurement basis permitted under GAAP, (ii) is irrevocable (unless a new election date occurs) and (iii) is applied only to entire instruments and not to portions of instruments. At September 30, 2014, December 31, 2013 and September 30, 2013, the Corporation had elected the fair value option on all of its residential mortgage loans held-for-sale. The Corporation has not elected the fair value option for any other financial assets or liabilities.
Share-Based Compensation	'
	Share-Based Compensation
	The Corporation grants stock options, stock awards, restricted stock performance units and restricted stock service-based units to certain executive and senior management employees. The Corporation accounts for share-based compensation expense using the modified-prospective transition method. Under that method, compensation expense is recognized for stock options based on the estimated grant date fair value as computed using the Black-Scholes option pricing model and the probability of issuance. The Corporation accounts for stock awards based on the closing stock price of the Corporation's common stock on the date of the award. The fair values of both stock options and stock awards are recognized as compensation expense on a straight-line basis over the requisite service period. The Corporation accounts for restricted stock performance units based on the closing stock price of the Corporation's common stock on the date of grant, discounted by the present value of estimated future dividends to be declared over the requisite performance or service period. The fair value of restricted stock performance units is recognized as compensation expense over the expected requisite performance period, or requisite service period for awards with multiple performance and service conditions. The Corporation accounts for restricted stock service-based units based on the closing stock price of the Corporation's common stock on the date of grant, as these awards accrue dividend equivalents equal to the amount of any cash dividends that would have been payable to a shareholder owning the number of shares of the Corporation's common stock represented by the restricted stock service-based units. The fair value of the restricted stock service-based units is recognized as compensation expense over the requisite service period.
	Cash flows realized from the tax benefits of exercised stock option awards that result from actual tax deductions that are in excess of the recorded tax benefits related to the compensation expense recognized for those options (excess tax benefits) are classified as financing activities on the consolidated statements of cash flows.
Income and Other Taxes	'
	Income and Other Taxes
	The Corporation is subject to the income and other tax laws of the United States, the State of Michigan and other states where nexus has been created. These laws are complex and are subject to different interpretations by the taxpayer and the various taxing authorities. In determining the provision for income and other taxes, management must make judgments and estimates about the application of these inherently complex laws, related regulations and case law. In the process of preparing the Corporation’s tax returns, management attempts to make reasonable interpretations of enacted tax laws. These interpretations are subject to challenge by the tax authorities upon audit or to reinterpretation based on management’s ongoing assessment of facts and evolving case law.
	On a quarterly basis, management assesses the reasonableness of its estimated annual effective federal tax rate based upon its current best estimate of taxable income and the applicable taxes expected for the full year. Deferred tax assets and liabilities are reassessed on a quarterly basis, including the need for a valuation allowance for deferred tax assets.
	Uncertain income tax positions are evaluated to determine whether it is more-likely-than-not that a tax position will be sustained upon examination based on the technical merits of the tax position. If a tax position is more-likely-than-not to be sustained, a tax benefit is recognized for the amount that is greater than 50% likely to be realized. Reserves for contingent income tax liabilities attributable to unrecognized tax benefits associated with uncertain tax positions are reviewed quarterly for adequacy based upon developments in tax law and the status of audits or examinations. The Corporation had no contingent income tax liabilities recorded at September 30, 2014, December 31, 2013 or September 30, 2013. The tax periods open to examination by the Internal Revenue Service include the calendar years ended December 31, 2013, 2012 and 2011.
Shareholders' Equity	'
	Shareholders’ Equity
	Common Stock Repurchase Programs
	From time to time, the board of directors of the Corporation approves common stock repurchase programs allowing management to repurchase shares of the Corporation’s common stock in the open market. The repurchased shares are available for later reissuance in connection with potential future stock dividends, the Corporation’s dividend reinvestment plan, employee benefit plans and other general corporate purposes. Under these programs, the timing and actual number of shares subject to repurchase are at the discretion of management and are contingent on a number of factors, including the projected parent company cash flow requirements and the Corporation’s market price per share.
	In January 2008, the board of directors of the Corporation authorized the repurchase of up to 500,000 shares of the Corporation’s common stock under a stock repurchase program. In November 2011, the board of directors of the Corporation reaffirmed the stock buy-back authorization with the qualification that the shares may only be repurchased if the share price is below the tangible book value per share of the Corporation’s common stock at the time of the repurchase. Since the January 2008 authorization, no shares have been repurchased. At September 30, 2014, there were 500,000 remaining shares available for repurchase under the Corporation’s stock repurchase programs.
	Underwritten Public Offerings of Common Stock
	On June 24, 2014, the Corporation issued and sold 2,500,000 shares of common stock at a public offering price of $28.00 per share. An additional 375,000 shares were issued and sold on June 30, 2014 upon the exercise in full of the underwriters' over-allotment option. The net proceeds from the issuance and sale of the common stock, after deducting the underwriting discount and issuance-related expenses, totaled $76.2 million.
	On September 18, 2013, the Corporation issued and sold 2,213,750 shares of common stock, including 288,750 shares of common stock that were issued and sold upon the exercise in full of the underwriters' over-allotment option, at a public offering price of $26.00 per share. The net proceeds from the issuance and sale of the common stock, after deducting the underwriting discount and issuance-related expenses, totaled $53.9 million.
	Shelf Registration
	On June 12, 2014, the Corporation filed an automatic shelf registration statement on Form S-3 with the Securities and Exchange Commission (SEC) for an indeterminate amount of securities, which became immediately effective. The shelf registration statement provides the Corporation with the ability to raise capital, subject to SEC rules and limitations, if the board of directors of the Corporation decides to do so. As previously discussed, the Corporation completed an $80.5 million public stock offering during the second quarter of 2014, which does not take into account the underwriting discount and issuance related expenses.
	The Corporation had previously filed a universal shelf registration statement with the SEC on May 23, 2013, which became effective on June 7, 2013, to register up to $100 million in securities. The Corporation's September 2013 common stock offering was completed under this universal shelf registration statement. Prior to filing its automatic shelf registration statement on June 12, 2014, the Corporation filed a post-effective amendment to terminate the effectiveness of the universal shelf registration statement and remove from registration all of the remaining securities covered by the universal shelf registration statement.
	Preferred Stock
	On April 20, 2009, the shareholders of the Corporation authorized the board of directors of the Corporation to issue up to 200,000 shares of preferred stock in connection with either an acquisition by the Corporation of an entity that has shares of preferred stock issued and outstanding pursuant to any program established by the United States government or participation by the Corporation in any program established by the United States government. At September 30, 2014, no shares of preferred stock were issued and outstanding.
Legal Matters	'
	Legal Matters
	The Corporation and Chemical Bank are subject to certain legal actions arising in the ordinary course of business. In the opinion of management, after consultation with legal counsel, the ultimate disposition of these matters is not expected to have a material adverse effect on the consolidated financial condition or results of operations of the Corporation.
Adopted Accounting Pronouncements	'
	Adopted Accounting Pronouncements
	Joint and Several Liability Arrangements
	In February 2013, the Financial Accounting Standards Board (FASB) issued ASU 2013-04, Liabilities (Topic 405): Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation is Fixed at the Reporting Date (ASU 2013-04). ASU 2013-04 provides guidance in relation to the recognition, measurement and disclosure of obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date. ASU 2013-04 is effective for interim and annual periods beginning after December 15, 2013 and should be applied retrospectively for all periods presented for those obligations resulting from joint and several liability arrangements that exist at the beginning of the fiscal year of adoption. The adoption of ASU 2013-04 as of January 1, 2014 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
	Accounting for Investments in Qualified Affordable Housing Projects
	In January 2014, the FASB issued ASU 2014-01, Investments—Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Qualified Affordable Housing Projects, a consensus of the FASB Emerging Issues Task Force (ASU 2014-01). ASU 2014-01 allows limited liability investors in qualified affordable housing projects to amortize the cost of their investment in proportion to tax credits and other tax benefits received (referred to as the "proportional amortization method"), and present the amortization as a component of income tax expense, as compared to the equity method, which requires the investment performance to be included in pre-tax income. The following conditions must be met in order for an investor to use the proportional amortization method: (i) it is probable that the tax credits allocable to the investor will be available, (ii) the investor does not have the ability to exercise significant influence over the operating and financial policies of the limited liability entity, (iii) substantially all of the projected benefits are from tax credits and other tax benefits, (iv) the investor's projected yield based solely on the cash flows from the tax credits and other tax benefits is positive, and (v) the investor is a limited liability investor in the limited liability entity for both legal and tax purposes, and the investor's liability is limited to its capital investment. The decision to apply the proportional amortization method is an accounting policy method that, if elected, must be applied consistently to all investments that meet the above conditions. An investor that does not qualify for the proportional amortization method or elects not to apply it will account for its investment under the cost or equity method in accordance with current guidance. ASU 2014-01 also introduces disclosure requirements for all investments in qualified affordable housing projects, regardless of the accounting method used for those investments. An investor must disclose (i) the nature of investments in qualified affordable housing projects and (ii) the effect of the measurement of those investments and the related tax credits on its financial statements. ASU 2014-01 is effective for public companies for interim and annual periods beginning after December 15, 2014, with early adoption permitted. Once adopted, the guidance must be applied retrospectively to all periods presented.
	The Corporation elected to early-adopt ASU 2014-01 as of January 1, 2014. The Corporation previously accounted for its investments in qualified affordable housing projects under the equity method; however, the Corporation determined that its investments in its qualified affordable housing projects meet the conditions set forth in ASU 2014-01 to account for these investments under the proportional amortization method. The Corporation invests in qualified affordable housing projects solely for the purpose of obtaining tax credits and other tax benefits. Accordingly, the Corporation believes that amortizing its investments in qualified affordable housing projects as a component of income tax expense rather than as a component of operating expenses better reflects the nature and intent of these investments. As a result of adopting ASU 2014-01, the Corporation recognized additional income tax expense attributable to the amortization of investments in qualified affordable housing projects of $0.1 million and $0.3 million during the three and nine months ended September 30, 2014, respectively. While the adoption of ASU 2014-01 requires retrospective application to all periods presented, the Corporation did not restate income tax expense for the three and nine months ended September 30, 2013 as the amount of additional income tax expense attributable to the amortization of investments in qualified affordable housing projects was not considered material. The Corporation's remaining investment in qualified affordable housing projects totaled $3.0 million at September 30, 2014, $3.2 million at December 31, 2013 and $3.3 million at September 30, 2013.
Pending Accounting Pronouncements	'
	Pending Accounting Pronouncements
	In-Substance Foreclosures
	In January 2014, the FASB issued ASU 2014-04, Receivables—Troubled Debt Restructurings by Creditors (Subtopic 310-40): Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure, a consensus of the FASB Emerging Issues Task Force (ASU 2014-04). ASU 2014-04 clarifies that an in-substance foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (i) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (ii) the borrower conveying all interest in the residential real estate property to the creditor to satisfy the loan through completion of a deed in lieu of foreclosure or similar legal agreement. ASU 2014-04 also requires disclosure of both the amount of foreclosed residential real estate property held by the creditor and the recorded investment in loans collateralized by residential real estate property that are in the process of foreclosure. ASU 2014-04 is effective for public companies for interim and annual periods beginning after December 15, 2014, with early adoption permitted. Once adopted, an entity can elect either (i) a modified retrospective transition method or (ii) a prospective transition method. The modified retrospective transition method is applied by means of a cumulative-effect adjustment to residential mortgage loans and foreclosed residential real estate properties existing as of the beginning of the period for which the amendments of ASU 2014-04 are effective, with real estate reclassified to loans measured at the carrying value of the real estate at the date of adoption and loans reclassified to real estate measured at the lower of net carrying value of the loan or the fair value of the real estate less costs to sell at the date of adoption. The prospective transition method is applied by means of applying the amendments of ASU 2014-04 to all instances of receiving physical possession of residential real estate properties that occur after the date of adoption. The adoption of ASU 2014-04 is not expected to have a material impact on the Corporation's consolidated financial condition or results of operations.
	Share-Based Compensation
	In June 2014, the FASB issued ASU 2014-12, Compensation—Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period, a consensus of the FASB Emerging Issues Task Force (ASU 2014-12). ASU 2014-12 requires that a performance target that affects vesting of share-based payment awards and that could be achieved after the requisite service period be treated as a performance condition. Compensation cost should be recognized in the period in which it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the periods for which the requisite service has already been rendered. If the performance target becomes probable of being achieved before the end of the requisite service period, the remaining unrecognized compensation cost should be recognized prospectively over the remaining requisite service period. The total amount of compensation cost recognized during and after the requisite service period should reflect the number of awards that are expected to vest and should be adjusted to reflect those awards that ultimately vest. The requisite service period ends when the employee can cease rendering service and still be eligible to vest in the award if the performance target is achieved. ASU 2014-12 is effective for all entities for interim and annual periods beginning after December 15, 2015, with early adoption permitted. An entity may apply the amendments in ASU 2014-12 either (i) prospectively to all awards granted or modified after the effective date or (ii) retrospectively to all awards with performance targets that are outstanding as of the beginning of the earliest annual period presented in the financial statements and to all new or modified awards thereafter. The adoption of ASU 2014-12 is not expected to have a material impact on the Corporation's consolidated financial condition or results of operations.
	Government-Guaranteed Mortgage Loans
	In August 2014, the FASB issued ASU 2014-14, Receivables—Troubled Debt Restructurings by Creditors (Subtopic 310-40): Classification of Certain Government Guaranteed Mortgage Loans upon Foreclosure, a consensus of the FASB Emerging Issues Task Force (ASU 2014-14). ASU 2014-14 provides clarifying guidance related to how creditors classify government-guaranteed loans upon foreclosure. Upon foreclosure of a government-guaranteed mortgage loan, the loan should be derecognized and a separate other receivable should be recognized if the following conditions are met: (i) the loan has a government guarantee that is not separable from the loan before foreclosure; (ii) at the time of foreclosure, the creditor has the intent to convey the real estate property to the guarantor and make a claim on the guarantee, and the creditor has the ability to recover under that claim; and (iii) at the time of foreclosure, any amount of the claim that is determined on the basis of the fair value of the real estate is fixed. The separate other receivable should be measured based on the amount of the loan balance (principal and interest) expected to be recovered from the guarantor at the time of foreclosure. ASU 2014-14 is effective for public companies for interim and annual periods beginning after December 15, 2014. An entity should adopt using either the modified retrospective method or the prospective transition method. An entity must apply the same method elected under ASU 2014-04. Early adoption is permitted if the entity has already adopted ASU 2014-04. The adoption of ASU 2014-14 is not expected to have a material impact on the Corporation's consolidated financial condition or results of operations.

Acquisitions_Tables

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Activity for accretable yield includes contractually due interest of acquired loans	'
	Activity for the accretable yield, which includes contractually due interest for acquired loans that have been renewed or extended since the date of acquisition and continue to be accounted for in loan pools in accordance with ASC 310-30, follows:
			Nine Months Ended
			September 30,
			2014			2013
			(In thousands)
	Balance at beginning of period		$	32,610		$	49,390
	Additions (reductions)*		4,493			(997		)
	Accretion recognized in interest income		(11,262		)	(13,235		)
	Reclassification from nonaccretable difference		10,000			125
	Balance at end of period		$	35,841		$	35,283
	*	Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.
	As part of its ongoing assessment of the acquired loan portfolio, management has determined that the overall credit quality of the acquired loan portfolio has improved, which has resulted in an improvement in expected cash flows of loan pools in the acquired commercial loan portfolio. Accordingly, management reclassified $10.0 million during the first quarter of 2014 from the nonaccretable difference to the accretable yield for these acquired commercial loan pools, which will increase amounts recognized into interest income over the estimated remaining lives of these loan pools.

Investment_Securities_Tables

Investment Securities (Tables)	9 Months Ended
	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]	'
Available-for-sale Securities	'
	The following is a summary of the amortized cost and fair value of investment securities available-for-sale and investment securities held-to-maturity at September 30, 2014, December 31, 2013 and September 30, 2013:
		Investment Securities Available-for-Sale
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	30-Sep-14
	Government sponsored agencies	$	76,626	$	354	$	42	$	76,938
	State and political subdivisions	39,589		1,375		—		40,964
	Residential mortgage-backed securities	252,908		846		2,715		251,039
	Collateralized mortgage obligations	141,273		346		1,174		140,445
	Corporate bonds	64,955		295		67		65,183
	Preferred stock	1,389		253		—		1,642
	Total	$	576,740	$	3,469	$	3,998	$	576,211
	31-Dec-13
	Government sponsored agencies	$	93,895	$	250	$	382	$	93,763
	State and political subdivisions	42,450		1,355		7		43,798
	Residential mortgage-backed securities	303,495		968		5,097		299,366
	Collateralized mortgage obligations	182,128		452		1,639		180,941
	Corporate bonds	65,028		499		252		65,275
	Preferred stock	1,389		63		25		1,427
	Total	$	688,385	$	3,587	$	7,402	$	684,570
	30-Sep-13
	Government sponsored agencies	$	86,065	$	264	$	404	$	85,925
	State and political subdivisions	44,191		1,386		5		45,572
	Residential mortgage-backed securities	310,550		1,144		3,534		308,160
	Collateralized mortgage obligations	200,407		199		2,148		198,458
	Corporate bonds	65,053		583		202		65,434
	Preferred stock	1,389		208		—		1,597
	Total	$	707,655	$	3,784	$	6,293	$	705,146
Held-to-maturity Securities	'
		Investment Securities Held-to-Maturity
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	30-Sep-14
	State and political subdivisions	$	308,062	$	5,704	$	6,476	$	307,290
	Trust preferred securities	10,500		—		3,515		6,985
	Total	$	318,562	$	5,704	$	9,991	$	314,275
	31-Dec-13
	State and political subdivisions	$	263,405	$	5,462	$	6,846	$	262,021
	Trust preferred securities	10,500		—		4,250		6,250
	Total	$	273,905	$	5,462	$	11,096	$	268,271
	30-Sep-13
	State and political subdivisions	$	272,079	$	5,978	$	8,441	$	269,616
	Trust preferred securities	10,500		—		4,250		6,250
	Total	$	282,579	$	5,978	$	12,691	$	275,866
Amortized cost and fair value of debt securities by contractual maturity	'
	The following is a summary of the amortized cost and fair value of investment securities at September 30, 2014, by maturity, for both available-for-sale and held-to-maturity investment securities. The maturities of residential mortgage-backed securities and collateralized mortgage obligations are based on scheduled principal payments. The maturities of all other debt securities are based on final contractual maturity.
		30-Sep-14
		Amortized		Fair Value
		Cost
		(In thousands)
	Investment Securities Available-for-Sale:
	Due in one year or less	$	153,539	$	153,302
	Due after one year through five years	349,258		348,952
	Due after five years through ten years	68,701		68,537
	Due after ten years	3,853		3,778
	Preferred stock	1,389		1,642
	Total	$	576,740	$	576,211
	Investment Securities Held-to-Maturity:
	Due in one year or less	$	34,833	$	34,898
	Due after one year through five years	135,150		136,359
	Due after five years through ten years	95,222		95,839
	Due after ten years	53,357		47,179
	Total	$	318,562	$	314,275
Summary of continuous unrealized loss position of securities	'
	The following schedule summarizes information for both available-for-sale and held-to-maturity investment securities with gross unrealized losses at September 30, 2014, December 31, 2013 and September 30, 2013, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position.
		Less Than 12 Months				12 Months or More				Total
		Fair		Gross		Fair		Gross		Fair		Gross
		Value		Unrealized		Value		Unrealized		Value		Unrealized
				Losses				Losses				Losses
		(In thousands)
	30-Sep-14
	Government sponsored agencies	$	1,744	$	4	$	24,810	$	38	$	26,554	$	42
	State and political subdivisions	91,532		4,010		70,116		2,466		161,648		6,476
	Residential mortgage-backed securities	34,280		144		196,045		2,571		230,325		2,715
	Collateralized mortgage obligations	44,195		81		28,544		1,093		72,739		1,174
	Corporate bonds	4,996		4		14,937		63		19,933		67
	Trust preferred securities	—		—		6,985		3,515		6,985		3,515
	Total	$	176,747	$	4,243	$	341,437	$	9,746	$	518,184	$	13,989
	31-Dec-13
	Government sponsored agencies	$	47,352	$	205	$	14,031	$	177	$	61,383	$	382
	State and political subdivisions	126,345		6,475		19,074		378		145,419		6,853
	Residential mortgage-backed securities	274,076		5,097		—		—		274,076		5,097
	Collateralized mortgage obligations	84,995		1,127		14,684		512		99,679		1,639
	Corporate bonds	14,931		78		19,826		174		34,757		252
	Trust preferred securities	—		—		6,250		4,250		6,250		4,250
	Preferred stock	1,024		25		—		—		1,024		25
	Total	$	548,723	$	13,007	$	73,865	$	5,491	$	622,588	$	18,498
	30-Sep-13
	Government sponsored agencies	$	43,816	$	223	$	14,395	$	181	$	58,211	$	404
	State and political subdivisions	120,232		6,918		30,915		1,528		151,147		8,446
	Residential mortgage-backed securities	267,495		3,532		40		2		267,535		3,534
	Collateralized mortgage obligations	129,049		1,617		15,302		531		144,351		2,148
	Corporate bonds	9,926		85		19,883		117		29,809		202
	Trust preferred securities	—		—		6,250		4,250		6,250		4,250
	Total	$	570,518	$	12,375	$	86,785	$	6,609	$	657,303	$	18,984

Loans_Tables

Loans (Tables)	9 Months Ended
	Sep. 30, 2014
Receivables [Abstract]	'
Summary of loans under portfolio	'
	A summary of loans follows:
			September 30,				December 31,				September 30,
			2014				2013				2013
			(In thousands)
	Commercial loan portfolio:
	Commercial		$	1,239,946			$	1,176,307			$	1,128,122
	Commercial real estate		1,322,646				1,232,658				1,215,631
	Real estate construction		125,782				89,795				78,361
	Land development		10,434				20,066				23,673
	Subtotal		2,698,808				2,518,826				2,445,787
	Consumer loan portfolio:
	Residential mortgage		984,049				960,423				942,777
	Consumer installment		783,443				644,769				622,040
	Home equity		574,620				523,603				512,067
	Subtotal		2,342,112				2,128,795				2,076,884
	Total loans		$	5,040,920			$	4,647,621			$	4,522,671
Recorded investment of loans in the commercial loan portfolio by risk rating categories	'
	The following schedule presents the recorded investment of loans in the commercial loan portfolio by risk rating categories at September 30, 2014, December 31, 2013 and September 30, 2013:
			Commercial				Commercial Real Estate				Real Estate				Land			Total
											Construction				Development
			(In thousands)
	30-Sep-14
	Originated Portfolio:
	Risk Grades 1-5		$	1,098,885			$	1,090,397			$	110,402			$	3,228		$	2,302,912
	Risk Grade 6		16,469				27,087				666				943			45,165
	Risk Grade 7		34,409				42,134				3,751				618			80,912
	Risk Grade 8		18,006				23,847				162				1,467			43,482
	Risk Grade 9		207				11				—				—			218
	Subtotal		1,167,976				1,183,476				114,981				6,256			2,472,689
	Acquired Portfolio:
	Risk Grades 1-5		58,342				130,887				10,801				2,303			202,333
	Risk Grade 6		3,909				2,086				—				—			5,995
	Risk Grade 7		5,885				6,197				—				148			12,230
	Risk Grade 8		3,834				—				—				1,727			5,561
	Risk Grade 9		—				—				—				—			—
	Subtotal		71,970				139,170				10,801				4,178			226,119
	Total		$	1,239,946			$	1,322,646			$	125,782			$	10,434		$	2,698,808
	31-Dec-13
	Originated Portfolio:
	Risk Grades 1-5		$	1,024,461			$	991,964			$	75,696			$	6,874		$	2,098,995
	Risk Grade 6		20,082				34,248				654				969			55,953
	Risk Grade 7		29,776				30,377				738				3,128			64,019
	Risk Grade 8		17,414				28,580				371				2,309			48,674
	Risk Grade 9		960				18				—				—			978
	Subtotal		1,092,693				1,085,187				77,459				13,280			2,268,619
	Acquired Portfolio:
	Risk Grades 1-5		73,763				133,653				12,336				4,667			224,419
	Risk Grade 6		5,472				5,022				—				—			10,494
	Risk Grade 7		852				7,792				—				—			8,644
	Risk Grade 8		3,527				1,004				—				2,119			6,650
	Risk Grade 9		—				—				—				—			—
	Subtotal		83,614				147,471				12,336				6,786			250,207
	Total		$	1,176,307			$	1,232,658			$	89,795			$	20,066		$	2,518,826
	30-Sep-13
	Originated Portfolio:
	Risk Grades 1-5		$	974,903			$	963,394			$	64,210			$	7,760		$	2,010,267
	Risk Grade 6		16,439				37,572				58				1,063			55,132
	Risk Grade 7		37,644				30,969				1,337				4,870			74,820
	Risk Grade 8		9,753				28,186				183				2,954			41,076
	Risk Grade 9		2,056				437				—				—			2,493
	Subtotal		1,040,795				1,060,558				65,788				16,647			2,183,788
	Acquired Portfolio:
	Risk Grades 1-5		82,648				141,234				12,573				4,604			241,059
	Risk Grade 6		2,620				4,837				—				—			7,457
	Risk Grade 7		992				7,847				—				—			8,839
	Risk Grade 8		1,067				1,155				—				2,422			4,644
	Risk Grade 9		—				—				—				—			—
	Subtotal		87,327				155,073				12,573				7,026			261,999
	Total		$	1,128,122			$	1,215,631			$	78,361			$	23,673		$	2,445,787
Recorded investment of loans in the consumer loan portfolio based on the credit risk profile of loans in a performing and nonperforming status	'
	The following schedule presents the recorded investment of loans in the consumer loan portfolio based on loans in a performing status and loans in a nonperforming status at September 30, 2014, December 31, 2013 and September 30, 2013:
			Residential Mortgage				Consumer				Home Equity				Total
							Installment								Consumer
			(In thousands)
	30-Sep-14
	Originated Loans:
	Performing		$	963,469			$	782,087			$	544,227			$	2,289,783
	Nonperforming		10,720				527				3,895				15,142
	Subtotal		974,189				782,614				548,122				2,304,925
	Acquired Loans:
	Performing		9,658				728				26,327				36,713
	Nonperforming		202				101				171				474
	Subtotal		9,860				829				26,498				37,187
	Total		$	984,049			$	783,443			$	574,620			$	2,342,112
	31-Dec-13
	Originated Loans:
	Performing		$	934,747			$	642,370			$	488,996			$	2,066,113
	Nonperforming		14,134				676				3,382				18,192
	Subtotal		948,881				643,046				492,378				2,084,305
	Acquired Loans:
	Performing		11,481				1,723				31,182				44,386
	Nonperforming		61				—				43				104
	Subtotal		11,542				1,723				31,225				44,490
	Total		$	960,423			$	644,769			$	523,603			$	2,128,795
	30-Sep-13
	Originated Loans:
	Performing		$	918,931			$	619,346			$	475,439			$	2,013,716
	Nonperforming		11,850				665				3,709				16,224
	Subtotal		930,781				620,011				479,148				2,029,940
	Acquired Loans:
	Performing		11,918				2,029				32,737				46,684
	Nonperforming		78				—				182				260
	Subtotal		11,996				2,029				32,919				46,944
	Total		$	942,777			$	622,040			$	512,067			$	2,076,884
Summary of nonperforming loans	'
	A summary of nonperforming loans follows:
			September 30,				December 31,				September 30,
			2014				2013				2013
			(In thousands)
	Nonaccrual loans:
	Commercial		$	18,213			$	18,374			$	11,809
	Commercial real estate		23,858				28,598				28,623
	Real estate construction		162				371				183
	Land development		1,467				2,309				2,954
	Residential mortgage		6,693				8,921				8,029
	Consumer installment		527				676				665
	Home equity		2,116				2,648				3,023
	Total nonaccrual loans		53,036				61,897				55,286
	Accruing loans contractually past due 90 days or more as to interest or principal payments:
	Commercial		16				536				281
	Commercial real estate		87				190				—
	Real estate construction		—				—				—
	Land development		—				—				—
	Residential mortgage		380				537				692
	Consumer installment		—				—				—
	Home equity		1,779				734				686
	Total accruing loans contractually past due 90 days or more as to interest or principal payments		2,262				1,997				1,659
	Nonperforming TDRs:
	Commercial loan portfolio		11,797				13,414				15,744
	Consumer loan portfolio		3,647				4,676				3,129
	Total nonperforming TDRs		15,444				18,090				18,873
	Total nonperforming loans		$	70,742			$	81,984			$	75,818
Schedule of Impaired loans by classes	'
	The following schedule presents impaired loans by classes of loans at September 30, 2014, December 31, 2013 and September 30, 2013:
			Recorded				Unpaid				Related
			Investment				Principal				Valuation
							Balance				Allowance
			(In thousands)
	30-Sep-14
	Impaired loans with a valuation allowance:
	Commercial		$	1,253			$	1,396			$	313
	Commercial real estate		3,779				4,094				862
	Real estate construction		—				—				—
	Land development		—				—				—
	Residential mortgage		19,629				19,629				328
	Subtotal		24,661				25,119				1,503
	Impaired loans with no related valuation allowance:
	Commercial		40,344				45,259				—
	Commercial real estate		45,550				59,037				—
	Real estate construction		162				369				—
	Land development		3,244				5,969				—
	Residential mortgage		6,693				6,693				—
	Consumer installment		527				527				—
	Home equity		2,116				2,116				—
	Subtotal		98,636				119,970				—
	Total impaired loans:
	Commercial		41,597				46,655				313
	Commercial real estate		49,329				63,131				862
	Real estate construction		162				369				—
	Land development		3,244				5,969				—
	Residential mortgage		26,322				26,322				328
	Consumer installment		527				527				—
	Home equity		2,116				2,116				—
	Total		$	123,297			$	145,089			$	1,503
	31-Dec-13
	Impaired loans with a valuation allowance:
	Commercial		$	2,517			$	2,656			$	728
	Commercial real estate		2,576				2,965				353
	Real estate construction		—				—				—
	Land development		—				—				—
	Residential mortgage		17,408				17,408				510
	Subtotal		22,501				23,029				1,591
	Impaired loans with no related valuation allowance:
	Commercial		38,838				44,377				—
	Commercial real estate		48,220				61,444				—
	Real estate construction		371				478				—
	Land development		7,170				11,817				—
	Residential mortgage		8,921				8,921				—
	Consumer installment		676				676				—
	Home equity		2,648				2,648				—
	Subtotal		106,844				130,361				—
	Total impaired loans:
	Commercial		41,355				47,033				728
	Commercial real estate		50,796				64,409				353
	Real estate construction		371				478				—
	Land development		7,170				11,817				—
	Residential mortgage		26,329				26,329				510
	Consumer installment		676				676				—
	Home equity		2,648				2,648				—
	Total		$	129,345			$	153,390			$	1,591
			Recorded				Unpaid				Related
			Investment				Principal				Valuation
							Balance				Allowance
			(In thousands)
	30-Sep-13
	Impaired loans with a valuation allowance:
Commercial		$	5,059			$	5,803			$	1,857
Commercial real estate		6,684				7,901				1,651
Real estate construction		183				253				33
Land development		517				653				97
Residential mortgage		17,731				17,731				585
Subtotal		30,174				32,341				4,223
Impaired loans with no related valuation allowance:
Commercial		21,543				25,642				—
Commercial real estate		43,178				57,256				—
Real estate construction		133				133				—
Land development		9,095				13,347				—
Residential mortgage		8,029				8,029				—
Consumer installment		665				665				—
Home equity		3,023				3,023				—
Subtotal		85,666				108,095				—
Total impaired loans:
Commercial		26,602				31,445				1,857
Commercial real estate		49,862				65,157				1,651
Real estate construction		316				386				33
Land development		9,612				14,000				97
Residential mortgage		25,760				25,760				585
Consumer installment		665				665				—
Home equity		3,023				3,023				—
Total		$	115,840			$	140,436			$	4,223
Schedule presents information related to impaired loans	'
	The following schedule presents information related to impaired loans for the three and nine months ended September 30, 2014 and 2013:
			Three Months Ended September 30, 2014								Nine Months Ended September 30, 2014
			Average				Interest Income				Average				Interest Income
			Recorded				Recognized				Recorded				Recognized
			Investment				While on				Investment				While on
							Impaired Status								Impaired Status
			(In thousands)
	Commercial		$	41,903			$	346			$	42,046			$	1,026
	Commercial real estate		50,133				263				51,571				990
	Real estate construction		162				—				164				—
	Land development		3,284				30				4,079				101
	Residential mortgage		26,166				310				26,561				941
	Consumer installment		481				—				630				—
	Home equity		2,246				—				2,212				—
	Total		$	124,375			$	949			$	127,263			$	3,058
			Three Months Ended September 30, 2013								Nine Months Ended September 30, 2013
			Average				Interest Income				Average				Interest Income
			Recorded				Recognized				Recorded				Recognized
			Investment				While on				Investment				While on
							Impaired Status								Impaired Status
			(In thousands)
	Commercial		$	27,025			$	215			$	26,894			$	633
	Commercial real estate		50,266				284				53,482				984
	Real estate construction		414				2				395				7
	Land development		9,615				79				10,470				261
	Residential mortgage		25,826				278				27,216				847
	Consumer installment		632				—				666				—
	Home equity		3,091				—				2,977				—
	Total		$	116,869			$	858			$	122,100			$	2,732
Schedule representing the aging status of the recorded investment in loans by classes	'
	The following schedule presents the aging status of the recorded investment in loans by classes of loans at September 30, 2014, December 31, 2013 and September 30, 2013:
			31-60				61-89				Accruing				Non-accrual			Total			Current		Total
			Days				Days				Loans				Loans			Past Due					Loans
			Past Due				Past Due				Past Due
											90 Days
											or More
			(In thousands)
	30-Sep-14
	Originated Portfolio:
	Commercial		$	3,717			$	1,145			$	16			$	18,213		$	23,091		$	1,144,885	$	1,167,976
	Commercial real estate		3,837				29				87				23,858			27,811			1,155,665		1,183,476
	Real estate construction		1,075				—				—				162			1,237			113,744		114,981
	Land development		—				—				—				1,467			1,467			4,789		6,256
	Residential mortgage		1,669				—				380				6,693			8,742			965,447		974,189
	Consumer installment		2,859				437				—				527			3,823			778,791		782,614
	Home equity		2,592				361				1,779				2,116			6,848			541,274		548,122
	Total		$	15,749			$	1,972			$	2,262			$	53,036		$	73,019		$	4,704,595	$	4,777,614
	Acquired Portfolio:
	Commercial		$	—			$	—			$	6,514			$	—		$	6,514		$	65,456	$	71,970
	Commercial real estate		—				—				1,559				—			1,559			137,611		139,170
	Real estate construction		—				—				—				—			—			10,801		10,801
	Land development		—				—				1,727				—			1,727			2,451		4,178
	Residential mortgage		—				—				202				—			202			9,658		9,860
	Consumer installment		—				—				—				—			—			829		829
	Home equity		335				—				227				—			562			25,936		26,498
	Total		$	335			$	—			$	10,229			$	—		$	10,564		$	252,742	$	263,306
			31-60				61-89				Accruing				Non-accrual			Total			Current		Total
			Days				Days				Loans				Loans			Past Due					Loans
			Past Due				Past Due				Past Due
											90 Days
											or More
			(In thousands)
	31-Dec-13
	Originated Portfolio:
	Commercial		$	4,748			$	865			$	536			$	18,374		$	24,523		$	1,068,170	$	1,092,693
	Commercial real estate		8,560				1,604				190				28,598			38,952			1,046,235		1,085,187
	Real estate construction		—				4,107				—				371			4,478			72,981		77,459
	Land development		—				—				—				2,309			2,309			10,971		13,280
	Residential mortgage		2,191				103				537				8,921			11,752			937,129		948,881
	Consumer installment		2,630				359				—				676			3,665			639,381		643,046
	Home equity		1,452				278				734				2,648			5,112			487,266		492,378
	Total		$	19,581			$	7,316			$	1,997			$	61,897		$	90,791		$	4,262,133	$	4,352,924
	Acquired Portfolio:
	Commercial		$	—			$	—			$	5,656			$	—		$	5,656		$	77,958	$	83,614
	Commercial real estate		—				133				1,695				—			1,828			145,643		147,471
	Real estate construction		—				—				—				—			—			12,336		12,336
	Land development		—				—				2,332				—			2,332			4,454		6,786
	Residential mortgage		—				—				61				—			61			11,481		11,542
	Consumer installment		3				51				—				—			54			1,669		1,723
	Home equity		394				—				43				—			437			30,788		31,225
	Total		$	397			$	184			$	9,787			$	—		$	10,368		$	284,329	$	294,697
	30-Sep-13
	Originated Portfolio:
	Commercial		$	7,833			$	1,542			$	281			$	11,809		$	21,465		$	1,019,330	$	1,040,795
	Commercial real estate		6,533				2,274				—				28,623			37,430			1,023,128		1,060,558
	Real estate construction		90				5,385				—				183			5,658			60,130		65,788
	Land development		187				—				—				2,954			3,141			13,506		16,647
	Residential mortgage		1,739				76				692				8,029			10,536			920,245		930,781
	Consumer installment		2,980				350				—				665			3,995			616,016		620,011
	Home equity		2,344				434				686				3,023			6,487			472,661		479,148
	Total		$	21,706			$	10,061			$	1,659			$	55,286		$	88,712		$	4,125,016	$	4,213,728
	Acquired Portfolio:
	Commercial		$	67			$	—			$	1,574			$	—		$	1,641		$	85,686	$	87,327
Commercial real estate		439				—				3,355				—			3,794			151,279		155,073
Real estate construction		—				—				—				—			—			12,573		12,573
Land development		—				—				2,422				—			2,422			4,604		7,026
Residential mortgage		264				—				77				—			341			11,655		11,996
Consumer installment		3				1				—				—			4			2,025		2,029
Home equity		389				79				182				—			650			32,269		32,919
Total		$	1,162			$	80			$	7,610			$	—		$	8,852		$	300,091	$	308,943
Schedule of Corporation's TDRs	'
	The following schedule presents the Corporation’s loans reported as TDRs at September 30, 2014, December 31, 2013 and September 30, 2013:
			Performing TDRs				Non-Performing TDRs				Nonaccrual TDRs				Total
			(In thousands)
	30-Sep-14
	Commercial loan portfolio		$	28,606			$	11,797			$	36,549			$	76,952
	Consumer loan portfolio		15,982				3,647				3,996				23,625
	Total		$	44,588			$	15,444			$	40,545			$	100,577
	31-Dec-13
	Commercial loan portfolio		$	26,839			$	13,414			$	31,961			$	72,214
	Consumer loan portfolio		12,732				4,676				5,321				22,729
	Total		$	39,571			$	18,090			$	37,282			$	94,943
	30-Sep-13
	Commercial loan portfolio		$	19,469			$	15,744			$	34,124			$	69,337
	Consumer loan portfolio		14,602				3,129				4,949				22,680
	Total		$	34,071			$	18,873			$	39,073			$	92,017
Schedule providing information on TDRs	'
	The following schedule provides information on the Corporation's TDRs that were modified during the three and nine months ended September 30, 2014 and 2013:
		Three Months Ended September 30, 2014											Nine Months Ended September 30, 2014
		Number			Pre-				Post-				Number			Pre-			Post-
		of Loans			Modification				Modification				of Loans			Modification			Modification
					Recorded				Recorded							Recorded			Recorded
					Investment				Investment							Investment			Investment
		(Dollars in thousands)
	Commercial loan portfolio:
	Commercial	7			$	448			$	448			34			$	12,379		$	12,379
	Commercial real estate	7			1,138				1,138				28			7,062			7,062
	Land development	—			—				—				1			72			72
	Subtotal – commercial loan portfolio	14			1,586				1,586				63			19,513			19,513
	Consumer loan portfolio	14			572				565				107			3,208			3,191
	Total	28			$	2,158			$	2,151			170			$	22,721		$	22,704
		Three Months Ended September 30, 2013 (As Revised)											Nine Months Ended September 30, 2013 (As Revised)
		Number			Pre-				Post-				Number			Pre-			Post-
		of Loans			Modification				Modification				of Loans			Modification			Modification
					Recorded				Recorded							Recorded			Recorded
					Investment				Investment							Investment			Investment
		(Dollars in thousands)
	Commercial loan portfolio:
	Commercial	6			$	716			$	716			25			$	5,075		$	5,075
	Commercial real estate	8			3,924				3,924				32			11,587			11,587
	Real estate construction	—			—				—				2			364			364
	Land development	—			—				—				4			1,958			1,958
	Subtotal – commercial loan portfolio	14			4,640				4,640				63			18,984			18,984
	Consumer loan portfolio	23			1,773				1,730				60			3,929			3,830
	Total	37			$	6,413			$	6,370			123			$	22,913		$	22,814
Troubled debt restructurings on financing receivables with defaults payment	'
	The following schedule includes TDRs for which there was a payment default during the three and nine months ended September 30, 2014 and 2013, whereby the borrower was past due with respect to principal and/or interest for 90 days or more, and the loan became a TDR during the twelve-month period prior to the default:
			Three Months Ended September 30, 2014							Nine Months Ended September 30, 2014
			Number of			Principal Balance at End of Period				Number of			Principal Balance at End of Period
			Loans							Loans
			(Dollars in thousands)
	Commercial loan portfolio:
	Commercial		—			$	—			6			$	875
	Commercial real estate		—			—				5			2,273
	Subtotal – commercial loan portfolio		—			—				11			3,148
	Consumer loan portfolio		4			162				7			242
	Total		4			$	162			18			$	3,390
			Three Months Ended September 30, 2013 (As Revised)							Nine Months Ended September 30, 2013 (As Revised)
			Number of			Principal Balance at End of Period				Number of			Principal Balance at End of Period
			Loans							Loans
			(Dollars in thousands)
	Commercial loan portfolio:
	Commercial		2			$	1,047			19			$	2,100
	Commercial real estate		4			3,614				5			3,740
	Real estate construction		—			—				1			160
	Land development		—			—				2			1,526
	Subtotal – commercial loan portfolio		6			4,661				27			7,526
	Consumer loan portfolio		6			142				15			645
	Total		12			$	4,803			42			$	8,171
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'
	The following schedule presents, by loan portfolio segment, the changes in the allowance for the three and nine months ended September 30, 2014 and details regarding the balance in the allowance and the recorded investment in loans at September 30, 2014 by impairment evaluation method.
			Commercial				Consumer				Unallocated				Total
			Loan				Loan
			Portfolio				Portfolio
			(In thousands)
	Changes in allowance for loan losses for the three months ended September 30, 2014:
	Beginning balance		$	44,224			$	29,565			$	4,004			$	77,793
	Provision for loan losses		715				834				(49		)		1,500
	Charge-offs		(1,733		)		(1,889		)		—				(3,622		)
	Recoveries		789				546				—				1,335
	Ending balance		$	43,995			$	29,056			$	3,955			$	77,006
	Changes in allowance for loan losses for the nine months ended September 30, 2014:
	Beginning balance		$	44,482			$	30,145			$	4,445			$	79,072
	Provision for loan losses		2,114				2,976				(490		)		4,600
	Charge-offs		(4,756		)		(5,713		)		—				(10,469		)
	Recoveries		2,155				1,648				—				3,803
	Ending balance		$	43,995			$	29,056			$	3,955			$	77,006
	Allowance for loan losses balance at September 30, 2014 attributable to:
	Loans individually evaluated for impairment		$	1,175			$	328			$	—			$	1,503
	Loans collectively evaluated for impairment		42,820				28,228				3,955				75,003
	Loans acquired with deteriorated credit quality		—				500				—				500
	Total		$	43,995			$	29,056			$	3,955			$	77,006
	Recorded investment (loan balance) at September 30, 2014:
	Loans individually evaluated for impairment		$	84,103			$	19,629			$	—			$	103,732
	Loans collectively evaluated for impairment		2,388,586				2,285,296				—				4,673,882
	Loans acquired with deteriorated credit quality		226,119				37,187				—				263,306
	Total		$	2,698,808			$	2,342,112			$	—			$	5,040,920
	The following schedule presents, by loan portfolio segment, details regarding the balance in the allowance and the recorded investment in loans at December 31, 2013 by impairment evaluation method.
			Commercial				Consumer				Unallocated				Total
			Loan				Loan
			Portfolio				Portfolio
			(In thousands)
	Allowance for loan losses balance at December 31, 2013 attributable to:
	Loans individually evaluated for impairment		$	1,081			$	510			$	—			$	1,591
	Loans collectively evaluated for impairment		43,401				29,135				4,445				76,981
	Loans acquired with deteriorated credit quality		—				500				—				500
	Total		$	44,482			$	30,145			$	4,445			$	79,072
	Recorded investment (loan balance) at December 31, 2013:
	Loans individually evaluated for impairment		$	89,905			$	17,408			$	—			$	107,313
	Loans collectively evaluated for impairment		2,178,714				2,066,897				—				4,245,611
	Loans acquired with deteriorated credit quality		250,207				44,490				—				294,697
	Total		$	2,518,826			$	2,128,795			$	—			$	4,647,621
	The following schedule presents, by loan portfolio segment, the changes in the allowance for the three and nine months ended September 30, 2013 and details regarding the balance in the allowance and the recorded investment in loans at September 30, 2013 by impairment evaluation method.
			Commercial				Consumer				Unallocated				Total
			Loan				Loan
			Portfolio				Portfolio
			(In thousands)
	Changes in allowance for loan losses for the three months ended September 30, 2013:
	Beginning balance		$	47,780			$	28,745			$	5,659			$	82,184
	Provision for loan losses		2,810				2,165				(1,975		)		3,000
	Charge-offs		(2,637		)		(1,793		)		—				(4,430		)
	Recoveries		374				404				—				778
	Ending balance		$	48,327			$	29,521			$	3,684			$	81,532
	Changes in allowance for loan losses for the nine months ended September 30, 2013:
	Beginning balance		$	49,975			$	29,333			$	5,183			$	84,491
	Provision for loan losses		5,815				4,684				(1,499		)		9,000
	Charge-offs		(9,374		)		(5,891		)		—				(15,265		)
	Recoveries		1,911				1,395				—				3,306
	Ending balance		$	48,327			$	29,521			$	3,684			$	81,532
	Allowance for loan losses balance at September 30, 2013 attributable to:
	Loans individually evaluated for impairment		$	3,638			$	585			$	—			$	4,223
	Loans collectively evaluated for impairment		44,689				28,436				3,684				76,809
	Loans acquired with deteriorated credit quality		—				500				—				500
Total		$	48,327			$	29,521			$	3,684			$	81,532
Recorded investment (loan balance) at September 30, 2013:
Loans individually evaluated for impairment		$	78,782			$	17,731			$	—			$	96,513
Loans collectively evaluated for impairment		2,105,006				2,012,209				—				4,117,215
Loans acquired with deteriorated credit quality		261,999				46,944				—				308,943
Total		$	2,445,787			$	2,076,884			$	—			$	4,522,671

Intangible_Assets_Tables

Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2014
Goodwill and Intangible Assets Disclosure [Abstract]	'
Net carrying value of intangible assets	'
	The following table shows the net carrying value of the Corporation’s intangible assets:
		September 30,			December 31,			September 30,
		2014			2013			2013
		(In thousands)
	Goodwill	$	120,164		$	120,164		$	120,164
	Other intangible assets:
	Core deposit intangible assets	$	8,665		$	10,001		$	10,466
	Mortgage servicing rights	3,293			3,423			3,399
	Total other intangible assets	$	11,958		$	13,424		$	13,865
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets	'
	The following table sets forth the carrying amount, accumulated amortization and amortization expense of core deposit intangible assets that are amortizable and arose from business combinations or other acquisitions:
		September 30,			December 31,			September 30,
		2014			2013			2013
		(In thousands)
	Gross original amount	$	18,659		$	18,659		$	18,659
	Accumulated amortization	9,994			8,658			8,193
	Carrying amount	$	8,665		$	10,001		$	10,466
	Amortization expense for the three months ended September 30	$	445					$	467
	Amortization expense for the nine months ended September 30	$	1,336					$	1,444
Net carrying value, fair value of MSRs and loans Corporation servicing for others	'
	The following shows the net carrying value and fair value of MSRs and the total loans that the Corporation is servicing for others:
		September 30,			December 31,			September 30,
		2014			2013			2013
		(In thousands)
	Net carrying value of MSRs	$	3,293		$	3,423		$	3,399
	Fair value of MSRs	$	6,618		$	6,878		$	6,839
	Loans serviced for others that have servicing rights capitalized	$	875,720		$	886,730		$	886,980
Activity for capitalized MSRs	'
	The following table shows the activity for capitalized MSRs:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
		(In thousands)
	Balance at beginning of period	$	3,344		$	3,421		$	3,423		$	3,478
	Additions	324			311			745			1,271
	Amortization	(375		)	(333		)	(875		)	(1,350		)
	Balance at end of period	$	3,293		$	3,399		$	3,293		$	3,399

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Loss (Tables)	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Components of accumulated other comprehensive loss, net of related tax benefit/expense	'
	The components of accumulated other comprehensive loss, net of related tax benefit/expense, were as follows:
		September 30,			December 31,			September 30,
		2014			2013			2013
		(In thousands)
	Net unrealized losses on investment securities – available-for-sale, net of related tax benefit of $185 at September 30, 2014, $1,335 at December 31, 2013 and $878 at September 30, 2013	$	(344	)	$	(2,480	)	$	(1,631	)
	Pension and other postretirement benefits adjustment, net of related tax benefit of $10,318 at September 30, 2014, $9,714 at December 31, 2013 and $18,062 at September 30, 2013	(19,162		)	(18,040		)	(33,544		)
	Accumulated other comprehensive loss	$	(19,506	)	$	(20,520	)	$	(35,175	)

Regulatory_Capital_Tables

Regulatory Capital (Tables)	9 Months Ended
	Sep. 30, 2014
Banking and Thrift [Abstract]	'
Corporation's and Chemical Bank's actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy	'
	The summary below compares the Corporation’s and Chemical Bank’s actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy:
		Actual				Minimum Required for Capital Adequacy Purposes				Required to be Well Capitalized Under Prompt Corrective Action Regulations
		Capital		Ratio		Capital		Ratio		Capital		Ratio
		Amount				Amount				Amount
		(Dollars in thousands)
	30-Sep-14
	Total Capital to Risk-Weighted Assets:
	Corporation	$	760,324	15	%	$	404,420	8	%	N/A		N/A
	Chemical Bank	613,673		12.2		403,840		8		$	504,799	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	696,963		13.8		202,210		4		N/A		N/A
	Chemical Bank	550,401		10.9		201,920		4		302,880		6
	Leverage Ratio:
	Corporation	696,963		11.1		251,133		4		N/A		N/A
	Chemical Bank	550,401		8.8		250,986		4		313,732		5
	31-Dec-13
	Total Capital to Risk-Weighted Assets:
	Corporation	$	649,836	14	%	$	371,465	8	%	N/A		N/A
	Chemical Bank	579,494		12.5		370,881		8		$	463,601	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	591,535		12.7		185,732		4		N/A		N/A
	Chemical Bank	521,283		11.2		185,440		4		278,160		6
	Leverage Ratio:
	Corporation	591,535		9.9		239,010		4		N/A		N/A
	Chemical Bank	521,283		8.7		238,884		4		298,605		5
	30-Sep-13
	Total Capital to Risk-Weighted Assets:
	Corporation	$	638,786	14.2	%	$	361,199	8	%	N/A		N/A
	Chemical Bank	568,626		12.6		360,617		8		$	450,771	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	582,039		12.9		180,600		4		N/A		N/A
	Chemical Bank	511,969		11.4		180,309		4		270,463		6
	Leverage Ratio:
	Corporation	582,039		10		232,972		4		N/A		N/A
	Chemical Bank	511,969		8.8		232,828		4		291,034		5

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Summary of assets measured at fair value on a recurring basis	'
	For assets measured at fair value on a recurring basis, quantitative disclosures about the fair value measurements for each major category of assets were as follows:
			Fair Value Measurements – Recurring Basis
			Quoted Prices			Significant			Significant			Total
			In Active			Other			Unobservable
			Markets for			Observable			Inputs
			Identical			Inputs			(Level 3)
			Assets			(Level 2)
			(Level 1)
			(In thousands)
	30-Sep-14
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—		$	76,938		$	—		$	76,938
	State and political subdivisions		—			40,964			—			40,964
	Residential mortgage-backed securities		—			251,039			—			251,039
	Collateralized mortgage obligations		—			140,445			—			140,445
	Corporate bonds		—			65,183			—			65,183
	Preferred stock		—			1,642			—			1,642
	Total investment securities – available-for-sale		—			576,211			—			576,211
	Loans held-for-sale		—			9,347			—			9,347
	Total assets measured at fair value on a recurring basis		$	—		$	585,558		$	—		$	585,558
	31-Dec-13
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—		$	93,763		$	—		$	93,763
	State and political subdivisions		—			43,798			—			43,798
	Residential mortgage-backed securities		—			299,366			—			299,366
	Collateralized mortgage obligations		—			180,941			—			180,941
	Corporate bonds		—			65,275			—			65,275
	Preferred stock		—			1,427			—			1,427
	Total investment securities – available-for-sale		—			684,570			—			684,570
	Loans held-for-sale		—			5,219			—			5,219
	Total assets measured at fair value on a recurring basis		$	—		$	689,789		$	—		$	689,789
	30-Sep-13
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—		$	85,925		$	—		$	85,925
	State and political subdivisions		—			45,572			—			45,572
	Residential mortgage-backed securities		—			308,160			—			308,160
	Collateralized mortgage obligations		—			198,458			—			198,458
	Corporate bonds		—			65,434			—			65,434
	Preferred stock		—			1,597			—			1,597
	Total investment securities – available-for-sale		—			705,146			—			705,146
	Loans held-for-sale		—			7,907			—			7,907
	Total assets measured at fair value on a recurring basis		$	—		$	713,053		$	—		$	713,053
Summary of assets measured at fair value on a nonrecurring basis	'
	For assets measured at fair value on a nonrecurring basis, quantitative disclosures about fair value measurements for each major category of assets were as follows:
			Fair Value Measurements – Nonrecurring Basis
			Quoted Prices			Significant			Significant			Total
			In Active			Other			Unobservable
			Markets for			Observable			Inputs
			Identical			Inputs			(Level 3)
			Assets			(Level 2)
			(Level 1)
			(In thousands)
	30-Sep-14
	Impaired originated loans		$	—		$	—		$	26,037		$	26,037
	Other real estate/repossessed assets		—			—			10,354			10,354
	Total		$	—		$	—		$	36,391		$	36,391
	31-Dec-13
	Impaired originated loans		$	—		$	—		$	28,852		$	28,852
	Other real estate/repossessed assets		—			—			9,776			9,776
	Total		$	—		$	—		$	38,628		$	38,628
	30-Sep-13
	Impaired originated loans		$	—		$	—		$	39,535		$	39,535
	Other real estate/repossessed assets		—			—			12,033			12,033
	Total		$	—		$	—		$	51,568		$	51,568
Summary of carrying amounts and estimated fair values of the financial instruments	'
	A summary of carrying amounts and estimated fair values of the Corporation’s financial instruments included in the consolidated statements of financial position was as follows:
		Level in Fair Value Measurement		30-Sep-14						31-Dec-13					30-Sep-13
		Hierarchy		Carrying			Fair			Carrying			Fair		Carrying		Fair
				Amount			Value			Amount			Value		Amount		Value
				(In thousands)
	Assets:
	Cash and cash equivalents	Level 1		$	382,138		$	382,138		$	310,788		$	310,788	$	493,110	$	493,110
	Investment securities:
	Available-for-sale	Level 2		576,211			576,211			684,570			684,570		705,146		705,146
	Held-to-maturity	Level 2		308,062			307,290			263,405			262,021		272,079		269,616
	Held-to-maturity	Level 3		10,500			6,985			10,500			6,250		10,500		6,250
	Nonmarketable equity securities	NA		25,572			25,572			25,572			25,572		25,572		25,572
	Loans held-for-sale	Level 2		9,347			9,347			5,219			5,219		7,907		7,907
	Net loans	Level 3		4,963,914			4,967,167			4,568,549			4,575,532		4,441,139		4,446,796
	Interest receivable	Level 2		17,057			17,057			15,748			15,748		16,359		16,359
	Liabilities:
	Deposits without defined maturities	Level 2		$	4,191,894		$	4,191,894		$	3,790,454		$	3,790,454	$	3,842,148	$	3,842,148
	Time deposits	Level 3		1,240,033			1,242,419			1,331,931			1,340,746		1,349,157		1,359,739
	Interest payable	Level 2		710			710			868			868		1,009		1,009
	Short-term borrowings	Level 2		323,086			323,086			327,428			327,428		357,595		357,595

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Numerator and denominator of the basic and diluted earnings per common share computations	'
	The following summarizes the numerator and denominator of the basic and diluted earnings per common share computations:
		Three Months Ended September 30,				Nine Months Ended September 30,
		2014		2013		2014		2013
		(In thousands, except per share data)
	Numerator for both basic and diluted earnings per common share, net income	$	16,767	$	14,993	$	46,816	$	42,430
	Denominator for basic earnings per common share, weighted average common shares outstanding	32,762		27,870		30,896		27,642
	Weighted average common stock equivalents	194		167		205		144
	Denominator for diluted earnings per common share	32,956		28,037		31,101		27,786
	Basic earnings per common share	$	0.51	$	0.54	$	1.52	$	1.54
	Diluted earnings per common share	0.51		0.53		1.51		1.53

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Summary of activity for Corporation's stock options	'
	A summary of activity for the Corporation’s stock options as of and for the nine months ended September 30, 2014 is presented below:
			Non-Vested						Stock Options Outstanding
			Stock Options Outstanding
			Number of		Weighted-		Weighted-		Number of		Weighted-
			Options		Average		Average		Options		Average
					Exercise		Grant Date				Exercise
					Price		Fair Value Per Share				Price
					Per Share						Per Share
	Outstanding at January 1, 2014		414,080		$	24.29	$	7.19	1,073,990		$	26.84
	Granted		190,011		29.45		9.64		190,011		29.45
	Exercised		—		—		—		(66,130	)	24.91
	Vested		(148,016	)	23.43		6.98		—		—
	Forfeited/expired		(14,869	)	25.69		7.8		(16,256	)	26.62
	Outstanding at September 30, 2014		441,206		$	26.75	$	8.3	1,181,615		$	27.37
	Exercisable/vested at September 30, 2014								740,409		$	27.75
Assumptions of Black-Scholes option pricing model	'
	The fair value of the stock options granted during the nine months ended September 30, 2014 was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions.
	Expected dividend yield	3		%
	Risk-free interest rate	2.16		%
	Expected stock price volatility	42.2		%
	Expected life of options – in years	7
	Weighted average fair value of options granted	$	9.64
Summary of activity for restricted stock performance units	'
	A summary of the activity for restricted stock units as of and for the nine months ended September 30, 2014 is presented below:
			Number of		Weighted-
			Units		Average
					Grant Date
					Fair Value
					Per Unit
	Outstanding at January 1, 2014		188,532		$	21.49
	Granted		68,619		27.49
	Converted into shares of common stock		(51,895	)	19.21
	Forfeited/expired		(4,813	)	23.84
	Outstanding at September 30, 2014		200,443		$	24.08

Pension_and_Other_Postretireme1

Pension and Other Postretirement Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan	'
	The components of net periodic benefit cost for the Corporation’s qualified and nonqualified pension plans and nonqualified postretirement benefit plan are as follows:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
		(In thousands)
	Defined Benefit Pension Plans
	Service cost	$	250		$	326		$	751		$	976
	Interest cost	1,312			1,166			3,936			3,500
	Expected return on plan assets	(2,078		)	(1,949		)	(6,235		)	(5,845		)
	Amortization of prior service credit	—			—			(1		)	(1		)
	Amortization of unrecognized net loss	569			946			1,707			2,838
	Net periodic benefit cost	$	53		$	489		$	158		$	1,468
	Postretirement Benefit Plan
	Service cost	$	5		$	5		$	14		$	14
	Interest cost	36			36			107			108
	Amortization of prior service cost	32			27			97			233
	Amortization of unrecognized net gain	(26		)	(18		)	(78		)	(55		)
	Net periodic benefit cost	$	47		$	50		$	140		$	300

Significant_Accounting_Policie2

Significant Accounting Policies (Details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Jun. 24, 2014	Dec. 31, 2013	Sep. 30, 2013	Sep. 18, 2013	23-May-13	Apr. 20, 2009	Jan. 31, 2008
		Bank
		Pools
Accounting Policies [Abstract]	'	'	'	'	'	'	'	'	'
Number of banks through which company operates	'	1	'	'	'	'	'	'	'
Number of regional banking units Chemical Bank operates through	'	4	'	'	'	'	'	'	'
Number of minimum days when principal or interest is past due is placed in nonaccrual category	'	'90 days	'	'	'	'	'	'	'
Number of minimum days in real estate residential loan when principal or interest is past due is placed in nonaccrual category	'	'120 days	'	'	'	'	'	'	'
Time period in which payments receive consistently and loans are returned to accrual status	'	'6 months	'	'	'	'	'	'	'
Number of pools of aggregate acquired loans based upon common risk characteristics	'	14	'	'	'	'	'	'	'
Time period sustained for payment history of principal and interest payments to move them to performing status	'	'6 months	'	'	'	'	'	'	'
Time period of real estate residential troubled debt restructurings reducing borrower's monthly payments by decreasing the interest rate charged on the loan	'	'24 months	'	'	'	'	'	'	'
Minimum number of days past due as to interest or principal payments in accruing loans moves to nonperforming loans	'	'90 days	'	'	'	'	'	'	'
Minimum amount of loan reviewed for detailed credit quality	'	$250,000	'	'	'	'	'	'	'
Time period for historical loan loss experience	'	'5 years	'	'	'	'	'	'	'
Minimum percentage of tax benefit is recognized for the amount likely to be realized	'	50.00%	'	'	'	'	'	'	'
Reserve for contingent income tax liabilities recorded	0	0	'	0	0	'	'	'	'
Number of shares authorized to be repurchased	'	'	'	'	'	'	'	'	500,000
Stock repurchased (shares)	'	0	'	'	'	'	'	'	'
Number of remaining shares authorized to be repurchased (shares)	500,000	500,000	'	'	'	'	'	'	'
Common Stock, Shares, Issued	32,762,591	32,762,591	2,500,000	29,789,825	29,778,250	2,213,750	'	'	'
CommonStockIssuedOverAllotment	'	'	375,000	'	'	288,750	'	'	'
Shares Issued, Price Per Share	'	'	$28	'	'	$26	'	'	'
Issuance of common stock, net of issuance costs	'	'	76,200,000	'	'	53,900,000	'	'	'
Stock Registered Under Universal Shelf Registration	'	'	'	'	'	'	100,000,000	'	'
Preferred stock, shares authorized	200,000	200,000	'	200,000	200,000	'	'	200,000	'
Preferred stock, shares issued	0	0	'	0	0	'	'	'	'
Preferred stock, shares outstanding	0	0	'	'	'	'	'	'	'
Expense related to qualified affordable housing projects	100,000	300,000	'	'	'	'	'	'	'
Remaining investment in qualified affordable housing projects	$3,000,000	$3,000,000	'	$3,200,000	$3,300,000	'	'	'	'

Acquisitions_Activity_for_Acqu

Acquisitions (Activity for Acquired Loans) (Details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013
Activity for accretable yield includes contractually due interest of acquired loans	'		'
Balance at beginning of period	$32,610		$49,390
Additions (reductions)	4,493	[1]	-997	[1]
Accretion recognized in interest income	-11,262		-13,235
Reclassification from nonaccretable difference	10,000		125
Balance at end of period	$35,841		$35,283
[1]	Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.

Acquisitions_Textual_Details

Acquisitions (Textual) (Details) (USD $)

9 Months Ended

3 Months Ended

9 Months Ended

0 Months Ended

0 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Mar. 10, 2014

Dec. 07, 2012

Dec. 07, 2012

Apr. 30, 2010

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Northwestern Bancorp, Inc. [Member]

Northwestern Bancorp, Inc. [Member]

Northwestern Bancorp, Inc. [Member]

Independent Bank [Member]

Independent Bank [Member]

OAK [Member]

OAK [Member]

OAK [Member]

OAK [Member]

Branches

Core Deposits [Member]

Offices

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Estimated purchase price for pending acquisition of Northwestern Bancorp, Inc.

'

'

'

'

'

$120,000,000

'

'

'

'

'

'

Business Acquisition, Transaction Costs

'

'

'

1,300,000

2,200,000

'

'

'

'

'

'

'

Number of branches acquired (branches)

'

'

'

'

'

'

21

'

'

'

'

'

Deposits acquired

'

'

'

'

'

'

404,000,000

'

'

'

'

'

Loans acquired

'

'

'

'

'

'

44,000,000

'

627,000,000

'

'

'

Acquisition purchase price

'

'

'

'

'

'

8,100,000

'

83,700,000

'

'

'

Premium paid on deposits purchased

'

'

'

'

'

'

11,500,000

'

'

'

'

'

Premium paid as a percentage of deposits purchased (percent)

'

'

'

'

'

'

2.85%

'

'

'

'

'

Discount on loans purchased (percent)

'

'

'

'

'

'

1.75%

'

'

'

'

'

Goodwill

120,164,000

120,164,000

120,164,000

'

'

'

6,800,000

'

'

'

'

'

Intangibles acquired

'

'

'

'

'

'

'

5,600,000

'

'

'

'

Service provided by acquiree bank through number of branches

'

'

'

'

'

'

'

'

14

'

'

'

Assets of acquiree company

'

'

'

'

'

'

'

'

820,000,000

'

'

'

Deposits of acquiree company

'

'

'

'

'

'

'

'

693,000,000

'

'

'

Brokered deposits of acquiree company

'

'

'

'

'

'

'

'

193,000,000

'

'

'

Contractually required principal payments of loan portfolio, acquisition date

'

'

'

'

'

'

'

'

683,000,000

'

'

'

Acquired loan portfolio acquisition date fair value

'

'

'

'

'

'

'

'

627,000,000

'

'

'

Outstanding contractual principal balance of acquired loan portfolio

'

'

'

'

'

'

'

'

'

286,000,000

320,000,000

334,000,000

Carrying amount of acquired loan portfolio

'

'

'

'

'

'

'

'

'

263,000,000

295,000,000

309,000,000

Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Reclassifications from Nonaccretable Difference

$10,000,000

$125,000

'

'

'

'

'

'

'

'

'

'

Investment_Securities_Summary_

Investment Securities (Summary of Amortized Cost and Fair Value of Available-For-Sale Investment Securities) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	$576,740	$688,385	$707,655
Investment securities available-for-sale, Unrealized Gains	3,469	3,587	3,784
Investment securities available-for-sale, Unrealized Losses	3,998	7,402	6,293
Available-for-sale Securities, Total	576,211	684,570	705,146
Government sponsored agencies [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	76,626	93,895	86,065
Investment securities available-for-sale, Unrealized Gains	354	250	264
Investment securities available-for-sale, Unrealized Losses	42	382	404
Available-for-sale Securities, Total	76,938	93,763	85,925
State and political subdivisions [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	39,589	42,450	44,191
Investment securities available-for-sale, Unrealized Gains	1,375	1,355	1,386
Investment securities available-for-sale, Unrealized Losses	0	7	5
Available-for-sale Securities, Total	40,964	43,798	45,572
Residential mortgage-backed securities [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	252,908	303,495	310,550
Investment securities available-for-sale, Unrealized Gains	846	968	1,144
Investment securities available-for-sale, Unrealized Losses	2,715	5,097	3,534
Available-for-sale Securities, Total	251,039	299,366	308,160
Collateralized Mortgage Obligations [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	141,273	182,128	200,407
Investment securities available-for-sale, Unrealized Gains	346	452	199
Investment securities available-for-sale, Unrealized Losses	1,174	1,639	2,148
Available-for-sale Securities, Total	140,445	180,941	198,458
Corporate bonds [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	64,955	65,028	65,053
Investment securities available-for-sale, Unrealized Gains	295	499	583
Investment securities available-for-sale, Unrealized Losses	67	252	202
Available-for-sale Securities, Total	65,183	65,275	65,434
Preferred stock [Member]	'	'	'
Available-for-sale Securities	'	'	'
Investment securities available-for-sale, Amortized Cost	1,389	1,389	1,389
Investment securities available-for-sale, Unrealized Gains	253	63	208
Investment securities available-for-sale, Unrealized Losses	0	25	0
Available-for-sale Securities, Total	$1,642	$1,427	$1,597

Investment_Securities_Summary_1

Investment Securities (Summary of Amortized Cost and Fair Value of Held-To-Maturity Investment Securities) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Held-to-maturity Securities	'	'	'
Investment securities held-to-maturity, Amortized Cost	$318,562	$273,905	$282,579
Investment securities held-to-maturity, Unrealized Gains	5,704	5,462	5,978
Investment securities held-to-maturity, Unrealized Losses	9,991	11,096	12,691
Total Held-to-maturity securities, Debt maturities, Fair Value	314,275	268,271	275,866
State and political subdivisions [Member]	'	'	'
Held-to-maturity Securities	'	'	'
Investment securities held-to-maturity, Amortized Cost	308,062	263,405	272,079
Investment securities held-to-maturity, Unrealized Gains	5,704	5,462	5,978
Investment securities held-to-maturity, Unrealized Losses	6,476	6,846	8,441
Total Held-to-maturity securities, Debt maturities, Fair Value	307,290	262,021	269,616
Trust Preferred Securities [Member]	'	'	'
Held-to-maturity Securities	'	'	'
Investment securities held-to-maturity, Amortized Cost	10,500	10,500	10,500
Investment securities held-to-maturity, Unrealized Gains	0	0	0
Investment securities held-to-maturity, Unrealized Losses	3,515	4,250	4,250
Total Held-to-maturity securities, Debt maturities, Fair Value	$6,985	$6,250	$6,250

Investment_Securities_Maturiti

Investment Securities (Maturities of Debt Securities) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Investment Securities Available-for-Sale:	'	'	'
Due in one year or less, Amortized Cost	$153,539	'	'
Due after one year through five years, Amortized Cost	349,258	'	'
Due after five years through ten years, Amortized Cost	68,701	'	'
Due after ten years, Amortized Cost	3,853	'	'
Preferred stock, Amortized Cost	1,389	'	'
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	576,740	'	'
Due in one year or less , Fair Value	153,302	'	'
Due after one year through five years, Fair Value	348,952	'	'
Due after five years through ten years, Fair Value	68,537	'	'
Due after ten years, Fair Value	3,778	'	'
Preferred stock, Fair Value	1,642	'	'
Total Available-for-sale securities, Debt maturities, Fair Value	576,211	'	'
Investment Securities Held-to-Maturity:	'	'	'
Due in one year or less, Amortized Cost	34,833	'	'
Due after one year through five years, Amortized Cost	135,150	'	'
Due after five years through ten years, Amortized Cost	95,222	'	'
Due after ten years, Amortized Cost	53,357	'	'
Total Held-to-maturity securities, Debt maturities, Amortized Cost	318,562	273,905	282,579
Due in one year or less , Fair Value	34,898	'	'
Due after one year through five years, Fair Value	136,359	'	'
Due after five years through ten years, Fair Value	95,839	'	'
Due after ten years, Fair Value	47,179	'	'
Total Held-to-maturity securities, Debt maturities, Fair Value	$314,275	$268,271	$275,866

Investment_Securities_Summary_2

Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	$176,747	$548,723	$570,518
Less Than 12 Months, Gross Unrealized Losses	4,243	13,007	12,375
12 Months or More, Fair Value	341,437	73,865	86,785
12 Months or More, Gross Unrealized Losses	9,746	5,491	6,609
Total, Fair Value	518,184	622,588	657,303
Total, Gross Unrealized Losses	13,989	18,498	18,984
Government sponsored agencies [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	1,744	47,352	43,816
Less Than 12 Months, Gross Unrealized Losses	4	205	223
12 Months or More, Fair Value	24,810	14,031	14,395
12 Months or More, Gross Unrealized Losses	38	177	181
Total, Fair Value	26,554	61,383	58,211
Total, Gross Unrealized Losses	42	382	404
State and political subdivisions [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	91,532	126,345	120,232
Less Than 12 Months, Gross Unrealized Losses	4,010	6,475	6,918
12 Months or More, Fair Value	70,116	19,074	30,915
12 Months or More, Gross Unrealized Losses	2,466	378	1,528
Total, Fair Value	161,648	145,419	151,147
Total, Gross Unrealized Losses	6,476	6,853	8,446
Residential mortgage-backed securities [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	34,280	274,076	267,495
Less Than 12 Months, Gross Unrealized Losses	144	5,097	3,532
12 Months or More, Fair Value	196,045	0	40
12 Months or More, Gross Unrealized Losses	2,571	0	2
Total, Fair Value	230,325	274,076	267,535
Total, Gross Unrealized Losses	2,715	5,097	3,534
Collateralized Mortgage Obligations [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	44,195	84,995	129,049
Less Than 12 Months, Gross Unrealized Losses	81	1,127	1,617
12 Months or More, Fair Value	28,544	14,684	15,302
12 Months or More, Gross Unrealized Losses	1,093	512	531
Total, Fair Value	72,739	99,679	144,351
Total, Gross Unrealized Losses	1,174	1,639	2,148
Corporate bonds [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	4,996	14,931	9,926
Less Than 12 Months, Gross Unrealized Losses	4	78	85
12 Months or More, Fair Value	14,937	19,826	19,883
12 Months or More, Gross Unrealized Losses	63	174	117
Total, Fair Value	19,933	34,757	29,809
Total, Gross Unrealized Losses	67	252	202
Trust Preferred Securities [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	0	0	0
Less Than 12 Months, Gross Unrealized Losses	0	0	0
12 Months or More, Fair Value	6,985	6,250	6,250
12 Months or More, Gross Unrealized Losses	3,515	4,250	4,250
Total, Fair Value	6,985	6,250	6,250
Total, Gross Unrealized Losses	3,515	4,250	4,250
Preferred Stock [Member]	'	'	'
Summary of continuous unrealized loss position of securities	'	'	'
Less Than 12 Months, Fair Value	'	1,024	'
Less Than 12 Months, Gross Unrealized Losses	'	25	'
12 Months or More, Fair Value	'	0	'
12 Months or More, Gross Unrealized Losses	'	0	'
Total, Fair Value	'	1,024	'
Total, Gross Unrealized Losses	'	$25	'

Investment_Securities_Textual_

Investment Securities (Textual) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]	'
Trust preferred investment securities held to maturity	$10.50
Trust preferred investment security of Non Public bank company	10
Interest in Trust preferred investment security	100.00%
Remaining trust preferred investment security of Non Public bank company	0.5
Interest in another trust preferred investment security	10.00%
Carrying value of trust preferred investment security one	10
Carrying value of trust preferred investment security two	0.5
Fair value of trust preferred investment security one	6.7
Fair value of trust preferred investment security two	0.3
Unrealized loss on trust preferred investment securities	3.5
Unrealized loss on trust preferred securities.	$3.50

Loans_Summary_of_Loans_Details

Loans (Summary of Loans) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Summary of loans under portfolio	'	'	'
Commercial loan	$2,698,808	$2,518,826	$2,445,787
Consumer loan	2,342,112	2,128,795	2,076,884
Total loans	5,040,920	4,647,621	4,522,671
Commercial [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Commercial loan	1,239,946	1,176,307	1,128,122
Real estate commercial [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Commercial loan	1,322,646	1,232,658	1,215,631
Real estate construction [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Commercial loan	125,782	89,795	78,361
Land development [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Commercial loan	10,434	20,066	23,673
Real estate residential [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Consumer loan	984,049	960,423	942,777
Consumer installment [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Consumer loan	783,443	644,769	622,040
Home equity [Member]	'	'	'
Summary of loans under portfolio	'	'	'
Consumer loan	$574,620	$523,603	$512,067

Loans_Summary_of_Recorded_Inve

Loans (Summary of Recorded Investment of Commercial Loans by Risk Rating Categories) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	$2,698,808	$2,518,826	$2,445,787
Commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,239,946	1,176,307	1,128,122
Real estate commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,322,646	1,232,658	1,215,631
Real estate construction [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	125,782	89,795	78,361
Land development [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	10,434	20,066	23,673
Originated Portfolio [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,472,689	2,268,619	2,183,788
Originated Portfolio [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,302,912	2,098,995	2,010,267
Originated Portfolio [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	45,165	55,953	55,132
Originated Portfolio [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	80,912	64,019	74,820
Originated Portfolio [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	43,482	48,674	41,076
Originated Portfolio [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	218	978	2,493
Originated Portfolio [Member] | Commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,167,976	1,092,693	1,040,795
Originated Portfolio [Member] | Commercial [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,098,885	1,024,461	974,903
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	16,469	20,082	16,439
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	34,409	29,776	37,644
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	18,006	17,414	9,753
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	207	960	2,056
Originated Portfolio [Member] | Real estate commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,183,476	1,085,187	1,060,558
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,090,397	991,964	963,394
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	27,087	34,248	37,572
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	42,134	30,377	30,969
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	23,847	28,580	28,186
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	11	18	437
Originated Portfolio [Member] | Real estate construction [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	114,981	77,459	65,788
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	110,402	75,696	64,210
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	666	654	58
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	3,751	738	1,337
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	162	371	183
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Originated Portfolio [Member] | Land development [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	6,256	13,280	16,647
Originated Portfolio [Member] | Land development [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	3,228	6,874	7,760
Originated Portfolio [Member] | Land development [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	943	969	1,063
Originated Portfolio [Member] | Land development [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	618	3,128	4,870
Originated Portfolio [Member] | Land development [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,467	2,309	2,954
Originated Portfolio [Member] | Land development [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	226,119	250,207	261,999
Acquired Portfolio [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	202,333	224,419	241,059
Acquired Portfolio [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	5,995	10,494	7,457
Acquired Portfolio [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	12,230	8,644	8,839
Acquired Portfolio [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	5,561	6,650	4,644
Acquired Portfolio [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	71,970	83,614	87,327
Acquired Portfolio [Member] | Commercial [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	58,342	73,763	82,648
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	3,909	5,472	2,620
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	5,885	852	992
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	3,834	3,527	1,067
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate commercial [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	139,170	147,471	155,073
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	130,887	133,653	141,234
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,086	5,022	4,837
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	6,197	7,792	7,847
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	1,004	1,155
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	10,801	12,336	12,573
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	10,801	12,336	12,573
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Land development [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	4,178	6,786	7,026
Acquired Portfolio [Member] | Land development [Member] | Risk Grades 1-5 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	2,303	4,667	4,604
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 6 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 7 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	148	0	0
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 8 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	1,727	2,119	2,422
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 9 [Member]	'	'	'
Recorded investment of loans in commercial loan portfolio by risk rating categories	'	'	'
Recorded investment (loan balance), Commercial, Total	$0	$0	$0

Loans_Summary_of_Recorded_Inve1

Loans (Summary of Recorded Investment of Consumer Loans by Risk Rating Categories) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	$2,342,112	$2,128,795	$2,076,884
Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	984,049	960,423	942,777
Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	783,443	644,769	622,040
Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	574,620	523,603	512,067
Originated Loans [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	2,304,925	2,084,305	2,029,940
Originated Loans [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	974,189	948,881	930,781
Originated Loans [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	782,614	643,046	620,011
Originated Loans [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	548,122	492,378	479,148
Originated Loans [Member] | Performing [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	2,289,783	2,066,113	2,013,716
Originated Loans [Member] | Performing [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	963,469	934,747	918,931
Originated Loans [Member] | Performing [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	782,087	642,370	619,346
Originated Loans [Member] | Performing [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	544,227	488,996	475,439
Originated Loans [Member] | Nonperforming [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	15,142	18,192	16,224
Originated Loans [Member] | Nonperforming [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	10,720	14,134	11,850
Originated Loans [Member] | Nonperforming [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	527	676	665
Originated Loans [Member] | Nonperforming [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	3,895	3,382	3,709
Acquired Loans [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	37,187	44,490	46,944
Acquired Loans [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	9,860	11,542	11,996
Acquired Loans [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	829	1,723	2,029
Acquired Loans [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	26,498	31,225	32,919
Acquired Loans [Member] | Performing [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	36,713	44,386	46,684
Acquired Loans [Member] | Performing [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	9,658	11,481	11,918
Acquired Loans [Member] | Performing [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	728	1,723	2,029
Acquired Loans [Member] | Performing [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	26,327	31,182	32,737
Acquired Loans [Member] | Nonperforming [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	474	104	260
Acquired Loans [Member] | Nonperforming [Member] | Real estate residential [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	202	61	78
Acquired Loans [Member] | Nonperforming [Member] | Consumer installment [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	101	0	0
Acquired Loans [Member] | Nonperforming [Member] | Home equity [Member]	'	'	'
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status	'	'	'
Recorded investment (loan balance), Consumer, Total	$171	$43	$182

Loans_Summary_of_Nonperforming

Loans (Summary of Nonperforming Loans) (Details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Summary of nonperforming loans	'	'	'
Total TDRs	$100,577	$94,943	$92,017
Total loans	5,040,920	4,647,621	4,522,671
Minimum number of days accruing loans past due move to nonaccrual status	'90 days	'	'
Commercial Loan Portfolio [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total TDRs	76,952	72,214	69,337
Total loans	2,698,808	2,518,826	2,445,787
Consumer Loan Portfolio [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total TDRs	23,625	22,729	22,680
Total loans	2,342,112	2,128,795	2,076,884
Nonperforming [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	53,036	61,897	55,286
Total accruing loans contractually past due 90 days or more as to interest or principal payments	2,262	1,997	1,659
Total TDRs	15,444	18,090	18,873
Total loans	70,742	81,984	75,818
Nonperforming [Member] | Commercial Loan Portfolio [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total TDRs	11,797	13,414	15,744
Nonperforming [Member] | Consumer Loan Portfolio [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total TDRs	3,647	4,676	3,129
Nonperforming [Member] | Commercial [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	18,213	18,374	11,809
Total accruing loans contractually past due 90 days or more as to interest or principal payments	16	536	281
Nonperforming [Member] | Real estate commercial [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	23,858	28,598	28,623
Total accruing loans contractually past due 90 days or more as to interest or principal payments	87	190	0
Nonperforming [Member] | Real Estate Construction Loans [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	162	371	183
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0	0
Nonperforming [Member] | Land Development Loans [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	1,467	2,309	2,954
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0	0
Nonperforming [Member] | Real estate residential [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	6,693	8,921	8,029
Total accruing loans contractually past due 90 days or more as to interest or principal payments	380	537	692
Nonperforming [Member] | Consumer Installment Loans [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	527	676	665
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0	0
Nonperforming [Member] | Home Equity Loans [Member]	'	'	'
Summary of nonperforming loans	'	'	'
Total nonaccrual loans	2,116	2,648	3,023
Total accruing loans contractually past due 90 days or more as to interest or principal payments	$1,779	$734	$686

Loans_Summary_of_Impaired_Loan

Loans (Summary of Impaired Loans by Classes of Loans) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	$24,661	$22,501	$30,174
Unpaid Principal Balance	25,119	23,029	32,341
Related Valuation Allowance	1,503	1,591	4,223
Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	98,636	106,844	85,666
Unpaid Principal Balance	119,970	130,361	108,095
Related Valuation Allowance	0	0	0
Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	123,297	129,345	115,840
Unpaid Principal Balance	145,089	153,390	140,436
Related Valuation Allowance	1,503	1,591	4,223
Commercial [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	1,253	2,517	5,059
Unpaid Principal Balance	1,396	2,656	5,803
Related Valuation Allowance	313	728	1,857
Commercial [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	40,344	38,838	21,543
Unpaid Principal Balance	45,259	44,377	25,642
Related Valuation Allowance	0	0	0
Commercial [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	41,597	41,355	26,602
Unpaid Principal Balance	46,655	47,033	31,445
Related Valuation Allowance	313	728	1,857
Real estate commercial [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	3,779	2,576	6,684
Unpaid Principal Balance	4,094	2,965	7,901
Related Valuation Allowance	862	353	1,651
Real estate commercial [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	45,550	48,220	43,178
Unpaid Principal Balance	59,037	61,444	57,256
Related Valuation Allowance	0	0	0
Real estate commercial [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	49,329	50,796	49,862
Unpaid Principal Balance	63,131	64,409	65,157
Related Valuation Allowance	862	353	1,651
Real estate construction [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	0	0	183
Unpaid Principal Balance	0	0	253
Related Valuation Allowance	0	0	33
Real estate construction [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	162	371	133
Unpaid Principal Balance	369	478	133
Related Valuation Allowance	0	0	0
Real estate construction [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	162	371	316
Unpaid Principal Balance	369	478	386
Related Valuation Allowance	0	0	33
Land development [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	0	0	517
Unpaid Principal Balance	0	0	653
Related Valuation Allowance	0	0	97
Land development [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	3,244	7,170	9,095
Unpaid Principal Balance	5,969	11,817	13,347
Related Valuation Allowance	0	0	0
Land development [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	3,244	7,170	9,612
Unpaid Principal Balance	5,969	11,817	14,000
Related Valuation Allowance	0	0	97
Real estate residential [Member] | Impaired loans with a valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	19,629	17,408	17,731
Unpaid Principal Balance	19,629	17,408	17,731
Related Valuation Allowance	328	510	585
Real estate residential [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	6,693	8,921	8,029
Unpaid Principal Balance	6,693	8,921	8,029
Related Valuation Allowance	0	0	0
Real estate residential [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	26,322	26,329	25,760
Unpaid Principal Balance	26,322	26,329	25,760
Related Valuation Allowance	328	510	585
Consumer installment [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	527	676	665
Unpaid Principal Balance	527	676	665
Related Valuation Allowance	0	0	0
Consumer installment [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	527	676	665
Unpaid Principal Balance	527	676	665
Related Valuation Allowance	0	0	0
Home equity [Member] | Impaired loans with no valuation allowance [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	2,116	2,648	3,023
Unpaid Principal Balance	2,116	2,648	3,023
Related Valuation Allowance	0	0	0
Home equity [Member] | Total Impaired Loans [Member]	'	'	'
Schedule of Impaired loans by classes	'	'	'
Recorded Investment	2,116	2,648	3,023
Unpaid Principal Balance	2,116	2,648	3,023
Related Valuation Allowance	$0	$0	$0

Loans_Summary_of_Information_R

Loans (Summary of Information Related to Impaired Loans) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	$124,375	$116,869	$127,263	$122,100
Interest income recognized related to loans with impaired status	949	858	3,058	2,732
Commercial [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	41,903	27,025	42,046	26,894
Interest income recognized related to loans with impaired status	346	215	1,026	633
Real estate commercial [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	50,133	50,266	51,571	53,482
Interest income recognized related to loans with impaired status	263	284	990	984
Real estate construction [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	162	414	164	395
Interest income recognized related to loans with impaired status	0	2	0	7
Land development [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	3,284	9,615	4,079	10,470
Interest income recognized related to loans with impaired status	30	79	101	261
Real estate residential [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	26,166	25,826	26,561	27,216
Interest income recognized related to loans with impaired status	310	278	941	847
Consumer installment [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	481	632	630	666
Interest income recognized related to loans with impaired status	0	0	0	0
Home equity [Member]	'	'	'	'
Schedule representing information related to impaired loans	'	'	'	'
Average recorded investment related to impaired loans	2,246	3,091	2,212	2,977
Interest income recognized related to loans with impaired status	$0	$0	$0	$0

Loans_Summary_of_the_Aging_Sta

Loans (Summary of the Aging Status of the Recorded Investment in Loans by Portfolio Segment/Class) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Originated Portfolio [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	$15,749	$19,581	$21,706
Financing receivable, recorded investment 61 to 89 days past due	1,972	7,316	10,061
Financing receivable, recorded investment accruing loans past due 90 days or more	2,262	1,997	1,659
Financing receivable, recorded investment, Nonaccrual loans	53,036	61,897	55,286
Financing receivable recorded investment, Total past due	73,019	90,791	88,712
Financing receivable, recorded investment, current	4,704,595	4,262,133	4,125,016
Financing receivable, recorded investment, Total loans	4,777,614	4,352,924	4,213,728
Originated Portfolio [Member] | Commercial [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	3,717	4,748	7,833
Financing receivable, recorded investment 61 to 89 days past due	1,145	865	1,542
Financing receivable, recorded investment accruing loans past due 90 days or more	16	536	281
Financing receivable, recorded investment, Nonaccrual loans	18,213	18,374	11,809
Financing receivable recorded investment, Total past due	23,091	24,523	21,465
Financing receivable, recorded investment, current	1,144,885	1,068,170	1,019,330
Financing receivable, recorded investment, Total loans	1,167,976	1,092,693	1,040,795
Originated Portfolio [Member] | Real estate commercial [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	3,837	8,560	6,533
Financing receivable, recorded investment 61 to 89 days past due	29	1,604	2,274
Financing receivable, recorded investment accruing loans past due 90 days or more	87	190	0
Financing receivable, recorded investment, Nonaccrual loans	23,858	28,598	28,623
Financing receivable recorded investment, Total past due	27,811	38,952	37,430
Financing receivable, recorded investment, current	1,155,665	1,046,235	1,023,128
Financing receivable, recorded investment, Total loans	1,183,476	1,085,187	1,060,558
Originated Portfolio [Member] | Real estate construction [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	1,075	0	90
Financing receivable, recorded investment 61 to 89 days past due	0	4,107	5,385
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	162	371	183
Financing receivable recorded investment, Total past due	1,237	4,478	5,658
Financing receivable, recorded investment, current	113,744	72,981	60,130
Financing receivable, recorded investment, Total loans	114,981	77,459	65,788
Originated Portfolio [Member] | Land development [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	0	0	187
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	1,467	2,309	2,954
Financing receivable recorded investment, Total past due	1,467	2,309	3,141
Financing receivable, recorded investment, current	4,789	10,971	13,506
Financing receivable, recorded investment, Total loans	6,256	13,280	16,647
Originated Portfolio [Member] | Real estate residential [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	1,669	2,191	1,739
Financing receivable, recorded investment 61 to 89 days past due	0	103	76
Financing receivable, recorded investment accruing loans past due 90 days or more	380	537	692
Financing receivable, recorded investment, Nonaccrual loans	6,693	8,921	8,029
Financing receivable recorded investment, Total past due	8,742	11,752	10,536
Financing receivable, recorded investment, current	965,447	937,129	920,245
Financing receivable, recorded investment, Total loans	974,189	948,881	930,781
Originated Portfolio [Member] | Consumer installment [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	2,859	2,630	2,980
Financing receivable, recorded investment 61 to 89 days past due	437	359	350
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	527	676	665
Financing receivable recorded investment, Total past due	3,823	3,665	3,995
Financing receivable, recorded investment, current	778,791	639,381	616,016
Financing receivable, recorded investment, Total loans	782,614	643,046	620,011
Originated Portfolio [Member] | Home equity [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	2,592	1,452	2,344
Financing receivable, recorded investment 61 to 89 days past due	361	278	434
Financing receivable, recorded investment accruing loans past due 90 days or more	1,779	734	686
Financing receivable, recorded investment, Nonaccrual loans	2,116	2,648	3,023
Financing receivable recorded investment, Total past due	6,848	5,112	6,487
Financing receivable, recorded investment, current	541,274	487,266	472,661
Financing receivable, recorded investment, Total loans	548,122	492,378	479,148
Acquired Portfolio [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	335	397	1,162
Financing receivable, recorded investment 61 to 89 days past due	0	184	80
Financing receivable, recorded investment accruing loans past due 90 days or more	10,229	9,787	7,610
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	10,564	10,368	8,852
Financing receivable, recorded investment, current	252,742	284,329	300,091
Financing receivable, recorded investment, Total loans	263,306	294,697	308,943
Acquired Portfolio [Member] | Commercial [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	0	0	67
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	6,514	5,656	1,574
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	6,514	5,656	1,641
Financing receivable, recorded investment, current	65,456	77,958	85,686
Financing receivable, recorded investment, Total loans	71,970	83,614	87,327
Acquired Portfolio [Member] | Real estate commercial [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	0	0	439
Financing receivable, recorded investment 61 to 89 days past due	0	133	0
Financing receivable, recorded investment accruing loans past due 90 days or more	1,559	1,695	3,355
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	1,559	1,828	3,794
Financing receivable, recorded investment, current	137,611	145,643	151,279
Financing receivable, recorded investment, Total loans	139,170	147,471	155,073
Acquired Portfolio [Member] | Real estate construction [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	0	0	0
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	0	0	0
Financing receivable, recorded investment, current	10,801	12,336	12,573
Financing receivable, recorded investment, Total loans	10,801	12,336	12,573
Acquired Portfolio [Member] | Land development [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	0	0	0
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	1,727	2,332	2,422
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	1,727	2,332	2,422
Financing receivable, recorded investment, current	2,451	4,454	4,604
Financing receivable, recorded investment, Total loans	4,178	6,786	7,026
Acquired Portfolio [Member] | Real estate residential [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	0	0	264
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	202	61	77
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	202	61	341
Financing receivable, recorded investment, current	9,658	11,481	11,655
Financing receivable, recorded investment, Total loans	9,860	11,542	11,996
Acquired Portfolio [Member] | Consumer installment [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	0	3	3
Financing receivable, recorded investment 61 to 89 days past due	0	51	1
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	0	54	4
Financing receivable, recorded investment, current	829	1,669	2,025
Financing receivable, recorded investment, Total loans	829	1,723	2,029
Acquired Portfolio [Member] | Home equity [Member]	'	'	'
Schedule representing the aging status of the recorded investment in loans by classes	'	'	'
Financing receivable, recorded investment 31 to 60 days past due	335	394	389
Financing receivable, recorded investment 61 to 89 days past due	0	0	79
Financing receivable, recorded investment accruing loans past due 90 days or more	227	43	182
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	562	437	650
Financing receivable, recorded investment, current	25,936	30,788	32,269
Financing receivable, recorded investment, Total loans	$26,498	$31,225	$32,919

Loans_Summary_of_TDRs_Details

Loans (Summary of TDRs) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Schedule of corporation's TDRs	'	'	'
Total TDRs	$100,577	$94,943	$92,017
Commercial Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	76,952	72,214	69,337
Consumer Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	23,625	22,729	22,680
Performing [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	44,588	39,571	34,071
Performing [Member] | Commercial Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	28,606	26,839	19,469
Performing [Member] | Consumer Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	15,982	12,732	14,602
Nonperforming [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	15,444	18,090	18,873
Nonperforming [Member] | Commercial Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	11,797	13,414	15,744
Nonperforming [Member] | Consumer Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	3,647	4,676	3,129
Substandard Nonaccrual [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	40,545	37,282	39,073
Substandard Nonaccrual [Member] | Commercial Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	36,549	31,961	34,124
Substandard Nonaccrual [Member] | Consumer Loan Portfolio [Member]	'	'	'
Schedule of corporation's TDRs	'	'	'
Total TDRs	$3,996	$5,321	$4,949

Loans_Summary_of_TDRs_Modified

Loans (Summary of TDRs Modified During the Period) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
	Loans	Loans	Loans	Loans
Schedule providing information on TDRs	'	'	'	'
Modified TDRs, Number of loans	28	37	170	123
Modified TDRs, Pre-modification recorded investment	$2,158	$6,413	$22,721	$22,913
Modified TDRs, Post-modification recorded investment	2,151	6,370	22,704	22,814
Subtotal-commercial loan portfolio [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on TDRs	'	'	'	'
Modified TDRs, Number of loans	14	14	63	63
Modified TDRs, Pre-modification recorded investment	1,586	4,640	19,513	18,984
Modified TDRs, Post-modification recorded investment	1,586	4,640	19,513	18,984
Consumer loan portfolio [Member] | Consumer Portfolio Segment [Member]	'	'	'	'
Schedule providing information on TDRs	'	'	'	'
Modified TDRs, Number of loans	14	23	107	60
Modified TDRs, Pre-modification recorded investment	572	1,773	3,208	3,929
Modified TDRs, Post-modification recorded investment	565	1,730	3,191	3,830
Commercial [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on TDRs	'	'	'	'
Modified TDRs, Number of loans	7	6	34	25
Modified TDRs, Pre-modification recorded investment	448	716	12,379	5,075
Modified TDRs, Post-modification recorded investment	448	716	12,379	5,075
Real estate commercial [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on TDRs	'	'	'	'
Modified TDRs, Number of loans	7	8	28	32
Modified TDRs, Pre-modification recorded investment	1,138	3,924	7,062	11,587
Modified TDRs, Post-modification recorded investment	1,138	3,924	7,062	11,587
Real Estate Construction Loans [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on TDRs	'	'	'	'
Modified TDRs, Number of loans	'	0	'	2
Modified TDRs, Pre-modification recorded investment	'	0	'	364
Modified TDRs, Post-modification recorded investment	'	0	'	364
Land development [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Schedule providing information on TDRs	'	'	'	'
Modified TDRs, Number of loans	0	0	1	4
Modified TDRs, Pre-modification recorded investment	0	0	72	1,958
Modified TDRs, Post-modification recorded investment	$0	$0	$72	$1,958

Loans_Summary_of_TDRs_with_a_P

Loans (Summary of TDRs with a Payment Default During the Period) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
	Loans	Loans	Loans	Loans
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	4	12	18	42
Financing receivable modification subsequent default recorded investment	$162	$4,803	$3,390	$8,171
Consumer Portfolio Segment [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	4	6	7	15
Financing receivable modification subsequent default recorded investment	162	142	242	645
Commercial [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	0	2	6	19
Financing receivable modification subsequent default recorded investment	0	1,047	875	2,100
Real estate commercial [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	0	4	5	5
Financing receivable modification subsequent default recorded investment	0	3,614	2,273	3,740
Real Estate Construction Loans [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	'	0	'	1
Financing receivable modification subsequent default recorded investment	'	0	'	160
Land Development Loans [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	'	0	'	2
Financing receivable modification subsequent default recorded investment	'	0	'	1,526
Subtotal-commercial loan portfolio [Member] | Commercial Loan Portfolio [Member]	'	'	'	'
Troubled debt restructurings on financing receivables with defaults payment	'	'	'	'
Financing receivable modifications subsequent default number of contract	0	6	11	27
Financing receivable modification subsequent default recorded investment	$0	$4,661	$3,148	$7,526

Loans_Schedule_of_the_Allowanc

Loans (Schedule of the Allowance for Loan Losses) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'	'	'	'	'
Beginning balance	$77,793	$82,184	$79,072	$84,491	'
Provision for loan losses	1,500	3,000	4,600	9,000	'
Charge-offs	-3,622	-4,430	-10,469	-15,265	'
Recoveries	1,335	778	3,803	3,306	'
Ending balance	77,006	81,532	77,006	81,532	'
Allowance for loan losses	'	'	'	'	'
Loans individually evaluated for impairment related to allowance for loan losses	1,503	4,223	1,503	4,223	1,591
Loans collectively evaluated for impairment related to allowance for loan losses	75,003	76,809	75,003	76,809	76,981
Loans acquired with deteriorated credit quality related to allowance for loan losses	500	500	500	500	500
Total	77,006	81,532	77,006	81,532	'
Loans individually evaluated for impairment related to recorded investment (loan balance)	103,732	96,513	103,732	96,513	107,313
Loans collectively evaluated for impairment related to recorded investment (loan balance)	4,673,882	4,117,215	4,673,882	4,117,215	4,245,611
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	263,306	308,943	263,306	308,943	294,697
Total loans	5,040,920	4,522,671	5,040,920	4,522,671	4,647,621
Commercial Loan Portfolio [Member]	'	'	'	'	'
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'	'	'	'	'
Beginning balance	44,224	47,780	44,482	49,975	'
Provision for loan losses	715	2,810	2,114	5,815	'
Charge-offs	-1,733	-2,637	-4,756	-9,374	'
Recoveries	789	374	2,155	1,911	'
Ending balance	43,995	48,327	43,995	48,327	'
Allowance for loan losses	'	'	'	'	'
Loans individually evaluated for impairment related to allowance for loan losses	1,175	3,638	1,175	3,638	1,081
Loans collectively evaluated for impairment related to allowance for loan losses	42,820	44,689	42,820	44,689	43,401
Loans acquired with deteriorated credit quality related to allowance for loan losses	0	0	0	0	0
Total	43,995	48,327	43,995	48,327	'
Loans individually evaluated for impairment related to recorded investment (loan balance)	84,103	78,782	84,103	78,782	89,905
Loans collectively evaluated for impairment related to recorded investment (loan balance)	2,388,586	2,105,006	2,388,586	2,105,006	2,178,714
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	226,119	261,999	226,119	261,999	250,207
Total loans	2,698,808	2,445,787	2,698,808	2,445,787	2,518,826
Consumer Loan Portfolio [Member]	'	'	'	'	'
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'	'	'	'	'
Beginning balance	29,565	28,745	30,145	29,333	'
Provision for loan losses	834	2,165	2,976	4,684	'
Charge-offs	-1,889	-1,793	-5,713	-5,891	'
Recoveries	546	404	1,648	1,395	'
Ending balance	29,056	29,521	29,056	29,521	'
Allowance for loan losses	'	'	'	'	'
Loans individually evaluated for impairment related to allowance for loan losses	328	585	328	585	510
Loans collectively evaluated for impairment related to allowance for loan losses	28,228	28,436	28,228	28,436	29,135
Loans acquired with deteriorated credit quality related to allowance for loan losses	500	500	500	500	500
Total	29,056	29,521	29,056	29,521	'
Loans individually evaluated for impairment related to recorded investment (loan balance)	19,629	17,731	19,629	17,731	17,408
Loans collectively evaluated for impairment related to recorded investment (loan balance)	2,285,296	2,012,209	2,285,296	2,012,209	2,066,897
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	37,187	46,944	37,187	46,944	44,490
Total loans	2,342,112	2,076,884	2,342,112	2,076,884	2,128,795
Unallocated [Member]	'	'	'	'	'
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	'	'	'	'	'
Beginning balance	4,004	5,659	4,445	5,183	'
Provision for loan losses	-49	-1,975	-490	-1,499	'
Charge-offs	0	0	0	0	'
Recoveries	0	0	0	0	'
Ending balance	3,955	3,684	3,955	3,684	'
Allowance for loan losses	'	'	'	'	'
Loans individually evaluated for impairment related to allowance for loan losses	0	0	0	0	0
Loans collectively evaluated for impairment related to allowance for loan losses	3,955	3,684	3,955	3,684	4,445
Loans acquired with deteriorated credit quality related to allowance for loan losses	0	0	0	0	0
Total	3,955	3,684	3,955	3,684	'
Loans individually evaluated for impairment related to recorded investment (loan balance)	0	0	0	0	0
Loans collectively evaluated for impairment related to recorded investment (loan balance)	0	0	0	0	0
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	0	0	0	0	0
Total loans	$0	$0	$0	$0	$0

Loans_Textual_Details

Loans (Textual) (Details) (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
	BaordOfDirectors
	Tenants
	Segment
	Loans
Loans (Textual) [Abstract]	'	'	'
Number of portfolio segment	2	'	'
Number of classes of loans	7	'	'
Number of tenants under lease of real estate	1	'	'
Number of members of the board of directors in loan committee	9	'	'
Minimum due period of loans consider in a nonperforming status	'90 days	'	'
Total nonaccrual TDR loans	$40,500,000	$39,100,000	$37,300,000
Difference between recorded investment and unpaid principal balance of loan	21,800,000	24,600,000	24,000,000
Confirmed losses (partial charge-offs)	18,200,000	21,200,000	20,200,000
Fair value of discount adjustment	3,600,000	3,400,000	3,800,000
Acquired impaired loans	10,200,000	7,600,000	9,800,000
Performing trouble debt restructuring under impaired loans	44,600,000	34,100,000	39,600,000
Financing receivable allowance for acquired loans	500,000	500,000	500,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Reclassifications from Nonaccretable Difference	10,000,000	125,000	'
Commercial Loan Portfolio [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Minimum value of loan requires executive and senior officer approval	1,500,000	'	'
Consumer Portfolio Segment [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Maximum due period of loans consider in performing status	'90 days	'	'
Minimum due period of loans consider in a nonperforming status	'90 days	'	'
Commercial [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Minimum value of loan requires group loan authority approval	1,000,000	'	'
Maximum value of loan requires executive and senior officer approval	3,500,000	'	'
Real Estate Residential Loans [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Period for loan secured under real estate residential security	'15 years	'	'
Loan-to-value ratio at the time of origination	80.00%	'	'
Land Development Loans [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Maximum period for payment of loan	'12 months	'	'
Maximum [Member] | Commercial Loan Portfolio [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Maximum value of loan requires group loan authority approval	5,000,000	'	'
Other loans requiring director loan committee approval depending on risk rating and credit action required	5,000,000	'	'
Maximum [Member] | Real Estate Residential Loans [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Upper limit of number of family residential properties	4	'	'
Minimum [Member] | Commercial Loan Portfolio [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Minimum value of loan requires group loan authority approval	1,000,000	'	'
Minimum value of loans depending on risk rating and requires credit action from board of directors	10,000,000	'	'
Minimum [Member] | Commercial [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Minimum value of loans requiring only director loan committee approval	$5,000,000	'	'
Minimum [Member] | Real Estate Residential Loans [Member]	'	'	'
Loans (Textual) [Abstract]	'	'	'
Lower limit of number of family residential properties	1	'	'

Intangible_Assets_Net_Carrying

Intangible Assets (Net Carrying Value) (Details) (USD $)	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Net carrying value of intangible assets	'	'	'	'	'	'
Goodwill	$120,164	'	$120,164	$120,164	'	'
Other intangible assets:	'	'	'	'	'	'
Total other intangible assets	11,958	'	13,424	13,865	'	'
Core deposit intangible assets [Member]	'	'	'	'	'	'
Other intangible assets:	'	'	'	'	'	'
Total other intangible assets	8,665	'	10,001	10,466	'	'
Mortgage servicing rights [Member]	'	'	'	'	'	'
Other intangible assets:	'	'	'	'	'	'
Total other intangible assets	$3,293	$3,344	$3,423	$3,399	$3,421	$3,478

Intangible_Assets_Amortization

Intangible Assets (Amortization Expense of Core Deposit Intangible Assets) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets	'	'	'	'	'
Carrying amount	$11,958	$13,865	$11,958	$13,865	$13,424
Amortization of intangible assets	'	'	2,211	2,794	'
Core deposit intangible assets [Member]	'	'	'	'	'
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets	'	'	'	'	'
Gross original amount	18,659	18,659	18,659	18,659	18,659
Accumulated amortization	9,994	8,193	9,994	8,193	8,658
Carrying amount	8,665	10,466	8,665	10,466	10,001
Amortization of intangible assets	$445	$467	$1,336	$1,444	'

Intangible_Assets_Carrying_and

Intangible Assets (Carrying and Fair Value of MSRs) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Net carrying value, fair value of MSRs and loans Corporation servicing for others	'	'	'
Loans serviced for others that have servicing rights capitalized	$875,720	$886,730	$886,980
Mortgage servicing rights [Member]	'	'	'
Net carrying value, fair value of MSRs and loans Corporation servicing for others	'	'	'
Net carrying value of MSRs	3,293	3,423	3,399
Fair value of MSRs	$6,618	$6,878	$6,839

Intangible_Assets_Activity_for

Intangible Assets (Activity for Capitalized MSRs) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Capitalized MSRs [Roll Forward]	'	'	'	'
Balance at beginning of period	'	'	$13,424	'
Amortization	'	'	-2,211	-2,794
Balance at end of period	11,958	13,865	11,958	13,865
Mortgage servicing rights [Member]	'	'	'	'
Capitalized MSRs [Roll Forward]	'	'	'	'
Balance at beginning of period	3,344	3,421	3,423	3,478
Additions	324	311	745	1,271
Amortization	-375	-333	-875	-1,350
Balance at end of period	$3,293	$3,399	$3,293	$3,399

Intangible_Assets_Textual_Deta

Intangible Assets (Textual) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Core deposit intangible assets [Member]	'	'	'
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]	'	'	'
2014	$400,000	'	'
2015	1,700,000	'	'
2016	1,500,000	'	'
2017	1,200,000	'	'
2018	1,200,000	'	'
2019 and thereafter	2,700,000	'	'
Mortgage servicing rights [Member]	'	'	'
Intangible Assets (Textual) [Abstract]	'	'	'
Impairment valuation allowance	$0	$0	$0

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Loss (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Components of accumulated other comprehensive loss, net of related tax benefit/expense	'	'	'
Net unrealized losses on investment securities – available-for-sale, net of related tax benefit of $185 at September 30, 2014, $1,335 at December 31, 2013 and $878 at September 30, 2013	($344)	($2,480)	($1,631)
Pension and other postretirement benefits adjustment, net of related tax benefit of $10,318 at September 30, 2014, $9,714 at December 31, 2013 and $18,062 at September 30, 2013	-19,162	-18,040	-33,544
Accumulated other comprehensive loss	($19,506)	($20,520)	($35,175)

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Loss (Textual) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Accumulated Other Comprehensive Loss (Textual) [Abstract]	'	'	'
Net unrealized gains (losses) on investment securities-available-for-sale, tax expense (benefit)	($185)	($1,335)	($878)
Pension and other postretirement benefits adjustment, tax benefit	$10,318	$9,714	$18,062

Regulatory_Capital_Details

Regulatory Capital (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]	'	'	'
Risk weighted assets	$5,060,000,000	$4,640,000,000	$4,510,000,000
Chemical Financial Corporation [Member]	'	'	'
Total Capital to Risk-Weighted Assets:	'	'	'
Actual, Capital Amount	760,324,000	649,836,000	638,786,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	404,420,000	371,465,000	361,199,000
Actual, Ratio	15.00%	14.00%	14.20%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%	8.00%
Tier 1 Capital to Risk-Weighted Assets:	'	'	'
Actual, Capital Amount	696,963,000	591,535,000	582,039,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	202,210,000	185,732,000	180,600,000
Actual, Ratio	13.80%	12.70%	12.90%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Leverage Ratio:	'	'	'
Actual, Capital Amount	696,963,000	591,535,000	582,039,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	251,133,000	239,010,000	232,972,000
Actual, Ratio	11.10%	9.90%	10.00%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Chemical Bank [Member]	'	'	'
Total Capital to Risk-Weighted Assets:	'	'	'
Actual, Capital Amount	613,673,000	579,494,000	568,626,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	403,840,000	370,881,000	360,617,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	504,799,000	463,601,000	450,771,000
Actual, Ratio	12.20%	12.50%	12.60%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%	8.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	10.00%	10.00%	10.00%
Tier 1 Capital to Risk-Weighted Assets:	'	'	'
Actual, Capital Amount	550,401,000	521,283,000	511,969,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	201,920,000	185,440,000	180,309,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	302,880,000	278,160,000	270,463,000
Actual, Ratio	10.90%	11.20%	11.40%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	6.00%	6.00%	6.00%
Leverage Ratio:	'	'	'
Actual, Capital Amount	550,401,000	521,283,000	511,969,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	250,986,000	238,884,000	232,828,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	$313,732,000	$298,605,000	$291,034,000
Actual, Ratio	8.80%	8.70%	8.80%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	5.00%	5.00%	5.00%

Fair_Value_Measurements_Fair_V

Fair Value Measurements (Fair Value of Assets on a Recurring Basis) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	$576,211	$684,570	$705,146
Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	576,211	684,570	705,146
Loans Held-for-sale	9,347	5,219	7,907
Total assets measured at fair value on a recurring basis	585,558	689,789	713,053
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Loans Held-for-sale	0	0	0
Total assets measured at fair value on a recurring basis	0	0	0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	576,211	684,570	705,146
Loans Held-for-sale	9,347	5,219	7,907
Total assets measured at fair value on a recurring basis	585,558	689,789	713,053
Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Loans Held-for-sale	0	0	0
Total assets measured at fair value on a recurring basis	0	0	0
Government sponsored agencies [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	76,938	93,763	85,925
Government sponsored agencies [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	76,938	93,763	85,925
Government sponsored agencies [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Government sponsored agencies [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	76,938	93,763	85,925
Government sponsored agencies [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
State and political subdivisions [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	40,964	43,798	45,572
State and political subdivisions [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	40,964	43,798	45,572
State and political subdivisions [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
State and political subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	40,964	43,798	45,572
State and political subdivisions [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Residential mortgage-backed securities [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	251,039	299,366	308,160
Residential mortgage-backed securities [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	251,039	299,366	308,160
Residential mortgage-backed securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Residential mortgage-backed securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	251,039	299,366	308,160
Residential mortgage-backed securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Collateralized mortgage obligations [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	140,445	180,941	198,458
Collateralized mortgage obligations [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	140,445	180,941	198,458
Collateralized mortgage obligations [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Collateralized mortgage obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	140,445	180,941	198,458
Collateralized mortgage obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Corporate bonds [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	65,183	65,275	65,434
Corporate bonds [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	65,183	65,275	65,434
Corporate bonds [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Corporate bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	65,183	65,275	65,434
Corporate bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Preferred stock [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	1,642	1,427	1,597
Preferred stock [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	1,642	1,427	1,597
Preferred stock [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	0	0	0
Preferred stock [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	1,642	1,427	1,597
Preferred stock [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]	'	'	'
Summary of assets measured at fair value on a recurring basis	'	'	'
Available-for-sale, at fair value	$0	$0	$0

Fair_Value_Measurements_Fair_V1

Fair Value Measurements (Fair Value of Assets on a Nonrecurring Basis) (Details) (Fair Value Measurements Nonrecurring [Member], USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	$36,391	$38,628	$51,568
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Significant Other Observable Inputs (Level 2) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Significant Unobservable Inputs (Level 3) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	36,391	38,628	51,568
Impaired originated loans [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	26,037	28,852	39,535
Impaired originated loans [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Impaired originated loans [Member] | Significant Other Observable Inputs (Level 2) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Impaired originated loans [Member] | Significant Unobservable Inputs (Level 3) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	26,037	28,852	39,535
Other real estate/repossessed assets [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	10,354	9,776	12,033
Other real estate/repossessed assets [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Other real estate/repossessed assets [Member] | Significant Other Observable Inputs (Level 2) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	0	0	0
Other real estate/repossessed assets [Member] | Significant Unobservable Inputs (Level 3) [Member]	'	'	'
Summary of assets measured at fair value on a nonrecurring basis	'	'	'
Total assets measured at fair value on a nonrecurring basis	$10,354	$9,776	$12,033

Fair_Value_Measurements_Schedu

Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments) (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Investment securities:	'	'	'
Available-for-sale	$576,211	$684,570	$705,146
Held-to-maturity	314,275	268,271	275,866
Carrying Amount [Member]	'	'	'
Investment securities:	'	'	'
Nonmarketable equity securities	25,572	25,572	25,572
Carrying Amount [Member] | Level 1[Member]	'	'	'
Assets:	'	'	'
Cash and cash equivalents	382,138	310,788	493,110
Carrying Amount [Member] | Level 2 [Member]	'	'	'
Investment securities:	'	'	'
Available-for-sale	576,211	684,570	705,146
Held-to-maturity	308,062	263,405	272,079
Loans Held-for-sale	9,347	5,219	7,907
Interest receivable	17,057	15,748	16,359
Liabilities:	'	'	'
Deposits without defined maturities	4,191,894	3,790,454	3,842,148
Interest payable	710	868	1,009
Short-term borrowings	323,086	327,428	357,595
Carrying Amount [Member] | Level 3 [Member]	'	'	'
Investment securities:	'	'	'
Held-to-maturity	10,500	10,500	10,500
Net loans	4,963,914	4,568,549	4,441,139
Liabilities:	'	'	'
Time deposits	1,240,033	1,331,931	1,349,157
Fair Value [Member]	'	'	'
Investment securities:	'	'	'
Nonmarketable equity securities	25,572	25,572	25,572
Fair Value [Member] | Level 1[Member]	'	'	'
Assets:	'	'	'
Cash and cash equivalents	382,138	310,788	493,110
Fair Value [Member] | Level 2 [Member]	'	'	'
Investment securities:	'	'	'
Available-for-sale	576,211	684,570	705,146
Held-to-maturity	307,290	262,021	269,616
Loans Held-for-sale	9,347	5,219	7,907
Interest receivable	17,057	15,748	16,359
Liabilities:	'	'	'
Deposits without defined maturities	4,191,894	3,790,454	3,842,148
Interest payable	710	868	1,009
Short-term borrowings	323,086	327,428	357,595
Fair Value [Member] | Level 3 [Member]	'	'	'
Investment securities:	'	'	'
Held-to-maturity	6,985	6,250	6,250
Net loans	4,967,167	4,575,532	4,446,796
Liabilities:	'	'	'
Time deposits	$1,242,419	$1,340,746	$1,359,739

Fair_Value_Measurements_Textua

Fair Value Measurements (Textual) (Details) (USD $)

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

In Thousands, unless otherwise specified

Core deposit intangible assets [Member]

Core deposit intangible assets [Member]

Core deposit intangible assets [Member]

Maximum [Member]

Minimum [Member]

Total Impaired Loans [Member]

Total Impaired Loans [Member]

Other Real Estate and Repossessed Assets [Member]

Other Real Estate and Repossessed Assets [Member]

Fair Value Measurements Recurring [Member]

Fair Value Measurements Recurring [Member]

Fair Value Measurements Recurring [Member]

Fair Value Measurements Nonrecurring [Member]

Fair Value Measurements Nonrecurring [Member]

Fair Value Measurements Nonrecurring [Member]

Maximum [Member]

Minimum [Member]

Maximum [Member]

Minimum [Member]

Fair Value Measurements (Textual) [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Liabilities recorded at fair value

'

'

'

'

'

'

'

'

'

'

'

'

$0

$0

$0

$0

$0

$0

Expected life of intangible assets

'

'

'

'

'

'

'15 years

'10 years

'

'

'

'

'

'

'

'

'

'

Percentage of discount factors used to determine fair value

'

'

'

'

'

'

'

'

80.00%

70.00%

75.00%

70.00%

'

'

'

'

'

'

Impairment of goodwill

0

0

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Impairment identified for intangible assets

'

'

'

$0

$0

$0

'

'

'

'

'

'

'

'

'

'

'

'

Earnings_Per_Common_Share_Deta

Earnings Per Common Share (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator and denominator of the basic and diluted earnings per common share computations	'	'	'	'
Numerator for both basic and diluted earnings per common share, net income	$16,767	$14,993	$46,816	$42,430
Denominator for basic earnings per common share, weighted average common shares outstanding	32,762,000	27,870,000	30,896,000	27,642,000
Weighted average common stock equivalents	194,000	167,000	205,000	144,000
Denominator for diluted earnings per common share	32,956,000	28,037,000	31,101,000	27,786,000
Basic earnings per common share (dollars per share)	$0.51	$0.54	$1.52	$1.54
Diluted earnings per common share (dollars per share)	$0.51	$0.53	$1.51	$1.53
Stock Option [Member]	'	'	'	'
Earnings Per Common Share (Textual) [Abstract]	'	'	'	'
Average number of exercisable employee stock option awards that were not included in the computation of diluted earnings per common share	249,150	308,009	251,403	377,847

ShareBased_Compensation_Stock_

Share-Based Compensation (Stock Option Activity) (Details) (USD $)	9 Months Ended
	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]	'
Weighted average fair value of options granted	$9.64
Stock Options [Member] | Non Vested [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'
Beginning balance, Number of Options	414,080
Granted, Number of Options	190,011
Exercised, Number of Options	0
Vested, Number of Options	-148,016
Forfeited/expired, Number of Options	-14,869
Ending balance, Number of Options	441,206
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'
Beginning balance, Weighted Average Exercise Price	$24.29
Granted, Weighted Average Exercise Price	$29.45
Exercised, Weighted Average Exercise Price	$0
Vested, Weighted Average Exercise Price	$23.43
Forfeited/expired, Weighted Average Exercise Price	$25.69
Ending balance, Weighted Average Exercise Price	$26.75
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]	'
Beginning balance, Weighted average grant date fair value	$7.19
Weighted average fair value of options granted	$9.64
Exercised, Weighted Average Grant Date Fair Value	$0
Vested, Weighted Average Grant Date Fair Value	$6.98
Forfeited/expired, Weighted Average Grant Date Fair Value	$7.80
Ending balance, Weighted average grant date fair value	$8.30
Stock Options [Member] | Vested & Nonvested [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'
Beginning balance, Number of Options	1,073,990
Granted, Number of Options	190,011
Exercised, Number of Options	-66,130
Vested, Number of Options	0
Forfeited/expired, Number of Options	-16,256
Ending balance, Number of Options	1,181,615
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'
Beginning balance, Weighted Average Exercise Price	$26.84
Granted, Weighted Average Exercise Price	$29.45
Exercised, Weighted Average Exercise Price	$24.91
Vested, Weighted Average Exercise Price	$0
Forfeited/expired, Weighted Average Exercise Price	$26.62
Ending balance, Weighted Average Exercise Price	$27.37
Stock Options [Member] | Vested [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]	'
Exercisable/vested, Number of Options	740,409
Exercisable/vested, Weighted Average Exercise Price	$27.75

ShareBased_Compensation_BlackS

Share-Based Compensation (Black-Scholes Pricing Model Assumptions) (Details) (USD $)	9 Months Ended
	Sep. 30, 2014
Assumptions of Black-Scholes option pricing model	'
Expected dividend yield	3.00%
Risk-free interest rate	2.16%
Expected stock price volatility	42.20%
Expected life of options - in years	'7 years 0 months 0 days
Weighted average fair value of options granted	$9.64

ShareBased_Compensation_Restri

Share-Based Compensation (Restricted Stock Unit Activity) (Details) (Restricted Stock Units (RSUs) [Member], USD $)	9 Months Ended
	Sep. 30, 2014
Restricted Stock Units (RSUs) [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Number of Shares [Roll Forward]	'
Beginning balance, Number of shares	188,532
Granted, Number of shares	68,619
Converted into shares of common stock, Number of shares	-51,895
Forfeited/expired, Number of shares	-4,813
Ending balance, Number of shares	200,443
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Weighted Average Grant Date Fair Value [Abstract]	'
Beginning balance, Weighted average grant date fair value	$21.49
Granted, Weighted Average grant date fair value	$27.49
Converted into shares of common stock, Weighted average grant date fair value	$19.21
Forfeited/expired, Weighted average grant date fair value	$23.84
Ending balance, Weighted average grant date fair value	$24.08

Textual_Details

(Textual) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Share-based compensation expense	$0.70	$0.80	$1.90	$2.10
Restricted Stock Units (RSUs) [Member]	'	'	'	'
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Corporation granted options to purchase restricted stock performance units	'	'	68,619	'
Unrecognized compensation expense	2.7	'	2.7	'
Unrecognized compensation expense, period of recognition	'	'	'2 years 7 months 6 days	'
Restricted Stock Units (RSUs) [Member] | Maximum [Member]	'	'	'	'
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Restricted stock performance units eligible to vest as a multiple of number of units granted	'	'	1.5	'
Restricted Stock Units (RSUs) [Member] | Minimum [Member]	'	'	'	'
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Restricted stock performance units eligible to vest as a multiple of number of units granted	'	'	0.25	'
Stock Option [Member]	'	'	'	'
Share-Based Compensation Plans (Textual) [Abstract]	'	'	'	'
Common stock available for future grants under share-based compensation plans	429,111	'	429,111	'
Weighted-average remaining contractual terms for outstanding stock options	'	'	'5 years 8 months 12 days	'
Weighted-average remaining contractual terms for exercisable stock options	'	'	'3 years 9 months 18 days	'
Outstanding in-the-money stock options, intrinsic value	2.2	'	2.2	'
Exercisable in-the-money stock options, intrinsic value	1.7	'	1.7	'
Closing price of common stock	$26.89	'	$26.89	'
Unrecognized compensation expense	$3	'	$3	'
Unrecognized compensation expense, period of recognition	'	'	'3 years 8 months 12 days	'

Pension_and_Other_Postretireme2

Pension and Other Postretirement Benefit Plans (Components of Net Periodic Benefit Cost (Income)) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Pension Plans [Member]	'	'	'	'
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan	'	'	'	'
Service cost	$250	$326	$751	$976
Interest cost	1,312	1,166	3,936	3,500
Expected return on plan assets	-2,078	-1,949	-6,235	-5,845
Amortization of prior service cost	0	0	-1	-1
Amortization of unrecognized net loss (gain)	569	946	1,707	2,838
Net periodic benefit cost	53	489	158	1,468
Postretirement Benefit Plan [Member]	'	'	'	'
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan	'	'	'	'
Service cost	5	5	14	14
Interest cost	36	36	107	108
Amortization of prior service cost	32	27	97	233
Amortization of unrecognized net loss (gain)	-26	-18	-78	-55
Net periodic benefit cost	$47	$50	$140	$300

Pension_and_Other_Postretireme3

Pension and Other Postretirement Benefit Plans (Textual) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Contribution to corporation's pension plan [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Contribution to defined benefit pension plan	'	'	'	$15
Pension Plans, Defined Benefit [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	'	'	5.00%	'
Chemical Financial Corporation [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Percentage of eligible pay contribution to certain employees	'	'	4.00%	'
Defined Contribution Plan, Employer Total Contribution Amount	$1	$0.90	$2.70	$2.70

Financial_Guarantees_Textual_D

Financial Guarantees (Textual) (Details) (Financial Standby Letter of Credit [Member], USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Financial Standby Letter of Credit [Member]	'	'	'
Financial Guarantees (Textual) [Abstract]	'	'	'
Letters of credit outstanding	$37	$47	$48
Expiration period for letters of credit, maximum	'5 years	'	'